XXVII. THE BIOLOGICAL SCIENCES ORGANIC EVOLUTION W. L. TOWER and JOHN G. SINCLAIR environmental control as it is practiced in Vienna is given in detail by Pzibram (Zeitschr. biol. Tecknik u. Methodik, III, 163-245). While employing material ostensibly of solely agricultural interest, the investigators in our agricultural experiment stations are in many cases dealing with strictly scientific as well as economic problems. General Survey of Activities.-The center of interest in problems of organic evolution during the year lies in three phases of heredity: the rôle of sex in inheritance, the behavior of hybrid characters, and the experimental modification of inheritance. Morgan in his recent book, Heredity and Sex (Columbia University Press), treats this heretofore bewildering mass of data simply and clearly. The view Adaptation. The interpretation of taken is a welcome aid to further natural phenomena received contribuwork even if incomplete. The work in tions from several sources during the heredity previous to 1913 is reviewed year. The decadent subject of mimicritically by Plate in the Vererbungs- cry and protective coloration is relehre (Leipzig, 1912). Both these vived on a somewhat more critical books contain excellent bibliographies. basis by Jacobi (Die Wissenschaft, Modification of inheritance is the most recent phase of the evolution problem and its treatment is fragmentary. The extent of investigations may be indicated by a few specific cases. Few investigators are in a position to carry out really critical experiments with incident forces. The University of Chicago has met the difficulty of conducting intensive research in evolution by more than doubling the capacity and equipment of its experimental plant; environmental control is a feature of this laboratory. The natural climatic complex at the Desert Botanical Laboratory in Tucson, Ariz., permits the conduct of mass experiments to compare with those at Chicago. At Cold Spring Harbor the collection of critical data on human inheritance is an important feature. New laboratories are being opened in England and on the Continent, prominent among which is the new Imperial Institute in Berlin; many good workers are preparing for an active investigation of heredity in this laboratory. The mechanics of XLVII). Adaptations of all sorts experienced a thoroughly mechanistic interpretation at the hands of Metcalf, Livingston, Henderson, Parker and Mathews in a "Symposium on Adaptation" (Am. Nat., XLVII, 65-116). They reflect well the attitude of present experimental biology. No other science has so long retained its teleological terminology as has biology, and it is refreshing to note the change in the type of investigations toward quantitative, analytic and synthetic work. A good working knowledge of the physical and mathematical sciences is becoming yearly more necessary in biological laboratories. Henderson's book, The Fitness of the Environment, presents the interacting system of the organism and its medium from this point of view. Verworn in his last edition of the General Physiology and again in his lectures on Irritability (Yale University Press, 1913) attacks the idea of causal factors in biological phenomena, noting the fact that any necessary condition to a reaction may be considered its cause if it is so desired. Shelford Morgan (Am. Nat., XLVII, 5-16) had applies the same idea to out of door nature (Animal Communities, University of Chicago Press, 1913). Any environmental factor may become a limiting factor for any organism effecting either its response or its very existence. Animal communities physiologically equivalent are thus maintained. This affords to some degree an explanation of geographical distribution as well as of local associa tions. a race of wingless flies among which one appeared with one wing. The race mutated from the normal wild fruit fly apparently by loss of a factor for wings. This case is offered as argument against the presence-absence hypothesis of unit characters in favor of a simple readjustment of the germinal complex. Heribert-Nilsson (Zeitschr. ind. Abst. Vererb., VIII, 90-231) has studied the variations of some pure lines of Oenothera lamarckiana, and obtained inheritable variants of all the characters which constitute the famous work of De Vries. Some were not so intense as these mutants and various gradations down to the normal were present. He claims that combinations of these variations give the mutant forms. That the synthesis of mutating stem stocks and fixed hybrids occurs in nature is open to little nomenon in evolution is debatable and a fit subject for experimental work. At present the origin of new species other than recombinations does not result from them. Better methods of studying variations disclose more mutations yearly. New types reported are: Safir for Drosophila (Biol. Centr., XXXII, 47-54), Kiessling for barley (Zeitschr. ind. Abst. Vererb., VIII, 48-78), and for the negro Castle and Simpson (Am. Nat., XLVII, 50-7). Cytology. The material basis of heredity continues to be a study largely of chromosomes, particular attention being paid to sexual differences of chromosome number. Wilson presents the study of "Heredity and Microscopic Research" (Science, XXXVII, 961) in a fairly dogmatic manner, pointing to the complete correlation of data from the field of cytology and breeding. Special studies of the X-doubt. The importance of this phechromosome in distinguishing sex and its linked characters are the subject of part of Morgan's Heredity and Sex, and of several articles. Sturtevant (Jour. Exper. Zool., XIV, 43-61) has formulated the lineal arrangement of hereditary factors along specific chromosomes of Drosophila, while Bridges (ibid., XV, 587-606) tries to explain a variation from the expected ratio in a case of sex linkage by reference to non-disjunction of the female Xchromosomes at maturation. Several studies on the chromosome complex in hybrids, the parent chromosomes being diverse, give the expected arrangement, and serve as a possible explanation of sterility or failure in development. It is, however, very difficult to evaluate the cytological evidence for heredity. That it confirms or helps to explain the data of breeding is quite true. Whether it will ever form the basis of predictions to experiment or will serve to open up new phases of breeding investigation is questionable. Variation. Mutation.-The necessity of "pure stock" is almost a truism among breeders, though the difficulty of a criterion for purity is apparent to those who study variation carefully. The chapter on meristic variations in Bateson's Problems of Genetics (Yale University Press, 1913) is worth noting in this connection. Inbreeding and Crossbreeding.-The effects of inbreeding are still debatable. Shull (Biol. Bull., XIV) gets degenerative effects in rotifers. Long continued experiments on protozoa, flies, beetles, and mammals show an inappreciable effect, except as inheritable weaknesses in both parents tend to become more fixed in the offspring. Calkins and Gregory in studying the later history of the progeny of exconjugants in Paramecium (Jour. Exper. Zool., XV, 467-527) find that each one is not a potential germ cell and therefore immortal as Weissman stated. Some die soon, some continue indefinitely without further conjugation, and to others periodic conjugation seems necessary to continued life. Jennings and Lashley (Jour. Exper. Zool., XIV, 393-466) find biparental inheritance of vigor and productivity among these forms. Crossbreeding undoubtedly invigorates a stock in most cases. Practical breeders like of hair and eye color (Brownlee, Proc. Webber, Marshall, and Anderson (Am. Roy. Soc. Edin., XXXII) have been Rogers Breeders' Mag., III), and Nilsson- discussed during the year. Ehle (Conf. int. de Genetique, IV) (Am. Breeders' Mag., III) has prestate that the main advances in all sented an extensive table of geneal(See also lines of practical breeding have been ogies of the feebleminded. through hybridization and extraction. XVI, Eugenics.) An extensive investigation of the his- Determination of Dominance and tological as well as apparent inherited Sex.--Dominance is reported by Cook characters of hybrid plants shows in- to be to some extent regulated extertermediate forms in 100 of the 121 nally in cotton breeding (Bur. Plant characters tabulated (H. B. Brown, Ind. Bull. 256). It is, moreover, not Miss. Agr. Exper. Sta., Tech. Bull., constant in corn, where an albino 3). It is found possible to state the mutant of yellow dent was at first degree of dominance quantitatively. dominant to yellow, later becoming reThe production of sterile hybrid stock cessive (Collins, Bur. Plant. Ind. Bull. may be avoided by the dilution of one 272). Richard Hertwig and Kusstrain in breeding back, if Detlefsen's chakewitch have revived the question results (Am. Breeders' Mag., III) are of sex determination (Biol. Centr., of general application. In crosses of XXXII). By preventing female frogs wild and domestic guinea pigs, what from laying their eggs for two or he calls one-eighth wild hybrids were three days after the normal period, fertile. That increased variability re- the percentage of males in the offsults from hybridizing ducks is shown spring was increased in some cases to by Philips (Jour. Exper. Zool., XII). 100 per cent., the normal ratio being The same result is not obtained one to one. Differential mortality does through conjugation in Paramecium. not explain the result when the total Davis (Am. Nat., XLVII. 449-77. 540-mortality is only five per cent. 64), while reporting progress in the hybrid synthesis of O. lamarckiana, has not yet produced a "mutating stem form." Mendelian principles have been successfully applied by Emerson and East to quantitative characters in maize (Neb. Agr. Exper. Sta. Bull. 2). Gametic coupling, with or without sex, forms at present an intricate chapter in breeding. Vilmorin (Jour. of Genetics, III, 67) reports that certain dwarf mutants in wheat while dominant to the normal can never be extracted pure, always giving 20 to 30 per cent. of tall progeny. In the researches of Tanaka (Jour. Coll. Agr. Tohohu Imperial Univ. Japan, V) and Toyama (Biol. Centr., XXXII) certain dominant characters of the silkworm show complete coupling or repulsion in the hybrids, depending on whether they are introduced through one or both parents. Eugenics consists at present largely of the study of human hybrids. Shuster has written a simple and general text on Eugenics (Oxford University Press), taking the stand that enough is known to warrant taking positive steps in applying eugenic principles. Traits of character (Woods, Am. Breeders' Mag., III) and the coupling It This is suggested that delayed fertilization XXIV). In Experimental Evolution. The question of the inheritance of acquired characters and the direct modification of germinal constitution have in practice become so closely allied that distinctions are purely academic. Sumner has produced modified forms in mice through the action of external temperatures, which persisted in inheritance. Now (Jour. Exper. Zoöl., XV, 315-79) he finds that internal temperatures of the mice are not disturbed by change of external temperatures beyond the individual fluctuations of the mice. Thus he believes the influence upon the germ plasm came indiThe salarectly through the soma. mander is polymorphic with regard Kammerer (Entw. Mech., to color. XXXVI) studies the effect of dry and moist atmospheric conditions on yel-power on particular carbohydrates are objects for mutation. A more interesting piece of original work is that of Stockard (Am. Nat., XLVII, 64183). This is a crucial test of the part played by alcoholism in inheritance. Stockard cites the marked action of alcohol on the reproductive tissues in general and the ovary in particular, producing a distinct atrophy in man. In the guinea pig the degenerative effect is not so apparent in the tissue, even after as much as three years of continual drunkenness, which is a large part of a guinea pig's life. The effects of intoxication are seen in the large number of failures, of stillborn litters and of stunted growth accompanied by extreme nervous disorders and early death. The second genera low and black pigment. Under moist conditions yellow predominates and in dry air the black. The induced changes are not obtained complete in a single generation. The change is reversible and here also several generations are necessary for the new equilibrium. Eisenberg (Umschau, 1912, pp. 805-7) records inheritable changes experimentally produced in cultures of bacteria, and Schiemann reports similar results for fungi (Zeit. ind. Abst. Vererb., VIII, 1-35). The work that Dobell reviews in summary (Jour. Genetics, II), while not accomplished in 1913, is made accessible for the first time. Among the protozoan blood parasites, the trypanosomes, mutants were produced. The agents employed were in one case tion while never intoxicated transdrugs of the pyronin, acridin and oxazine groups, and the corresponding mutants were changed in virulence as well as in form. In one case reported, by experimental means the mutant was made to revert, after many gen- Up to this time the conditions of erations, to the original form. Others experiment have resulted in mutative made resistant to arsenic by treatment changes whose nature seems solely dewith arsenophenylglycin through a termined by the organism itself. Incinumber of generations, retain this char- dent forces have apparently no deteracter hereditarily thereafter. Trans- minative or directive effects other than ference through cold-blooded animals that shown by general degeneration. permanently alters certain races of Future investigations will deal more trypanosomes. Similar cases are re-intimately with the physiology of the ported for bacteria, where color, im- hereditary mechanism under the acmunity, virulence, and fermenting tion of controlled external forces. mits its failings apparently in an accentuated degree. The most potent effect of alcoholic taint in these stocks is a debilitated nervous system and defective sense organs. ZOOLOGY H. E. JORDAN Morphology.-Buxton (Zoöl. Jahrb. Supp., XIV, 2) has published an elaborately illustrated comparative morphologic and histologic study of the coxal glands of spiders and allies (arachnids). He shows an homology of the salivary gland in Peripatus with the coxal gland of the solifugae; also an homology of the coxal glands of other arachnids with the large nephridia of Peripatus on legs four and five. The question as to whether the segmentation of the vertebrate body expressed in the primitive somites of the embryo and certain definitive structures in the adult extends anteriorly over the head, at least in early stages, has long been a problem of much interest to morphologists. A contribution is made to the subject by Johnson (Am. Jour. Anat., XIV, 2), who shows that in embryos of Chelydra serpentina (the snapping turtle) three preotic head somites are developed on each side, and traces their development into their respective adult derivatives. The function of the interstitial cells of the testis still awaits solution. These cells are supposed by many to elaborate an internal secretion which has to do with the origin and maintenance of male secondary sexual characters. Whitehead (Anat. Rec., VII, 3) makes a notable contribution to this subject from a study of a tes- | Weidenreich, of the hypothesis that tis from a human pseudohermaphro- the granules of eosinophile leucocytes dite with female sex characters, the are of exogenous origin) and degenresults of which are strongly opposed erated muscle tissue. The opposing to the theory which attributes the de- view attributes an endogenous origin velopment of secondary sex characters to the eosinophile granules. This view to these cells (see also XXX, Anat- finds support in the observation by Joromy). Goodale (Am. Nat., XLVII, dan and Flippin (Folia Hæmatologica, 555) has put the theory to experi- XV) that in the turtle, eosinophile mental test. He removed the ovaries granulocytes appear before hæmoand testes from young Brown Leg- globin-containing blood cells. This horns. The results of his experiments show that the female may assume male characters following the removal of the ovary, but that the male assumes no positive female characters after removal of the testes. The changes in secondary sexual characters in the castrated male are interpreted as a return to the juvenile condition. These experiments seem to indicate that the interstitial cells of the testes bear no causal relationship to secondary sexual characters, and suggest, furthermore, that the condition of femaleness is of the nature of inhibited maleness. Pappenheimer (Am. Jour. Anat., XIV, 3) has continued his histological study of the thymus. In the frog's thymus, by the use of Benda's mitochondrial method, he is able to demonstrate minute granules not hitherto described. Similar granules, probably mitochondria, were also demonstrable by the use of vital stains in living cells. On the basis of an identical granular content, he identifies the small thymic cells as lymphocytes which have wandered in from the blood (thus confirming Maximow in his findings in amphibia), an important observation in that it is in direct opposition to a view widely held that the small thymic cells are differentiated epithelial cells of the original anlagen. contribution, furthermore, presents evidence to show that the monophyletic theory of blood-cell origin holds in turtles, that is, all types of blood cells, red, white, and lymphocytes, trace their ancestry back to a common blood mother-cell, the "lymphocyte" of Maximow. The spindle cells are shown to have a double origin from endothelial cells and from small lymphocytes. Superfœtation, or the possibility of a second successful fertilization before the termination of a pregnancy, has long been a mooted question. A few instances of probable superfotation in man are on record. King (Biol. Bull., XXIV, 6) records observations on this important point made in the course of a series of inbreeding experiments with the albino rat. Superfætation is said to occur occasionally and causes an interval of two or three days between the birth of different members of a litter. In rare instances ovulation takes place in the albino rat during pregnancy and superfœtation occurs. King reports two cases of this kind in which litters have been produced at intervals of about two weeks. A much debated question concerns the possibility of mammalian ova to develop parthenogenetically, that is, without fertilization. Parthenogenetic development normally occurs in cerEmbryology. Badertscher (A m. tain lower forms, for example, the bee, Jour. Anat., XV, 1) has shown from where the unfertilized egg gives rise a study of muscle degeneration into the male or drone. Reputed partheamphibia that the eosinophile granules of eosinophile leucocytes are products of degenerated muscle tissue and degenerated red blood cells. The principal constituent of the granules is conceived to be hæmoglobin. Accord ing to this view eosinophile leucocytes are simply white blood cells ingested with degenerated erythrocytes (also the view of the chief recent exponent, nogenetic development of human ova has been held responsible for ovarian tumors. Newman's (Biol. Bull., XXV, 1) evidence on this point is therefore of special importance. He has demonstrated parthenogenetic cleavage in the armadillo ovum. These ova never leave the ovary and evidently do not undergo development beyond the eightcell stage, after which they degenerate |