Februakt 4, 1916] 



SCIENCE 



179 



My later studies, extending over a period of 

 more than ten years, afford abundant confirmatory 

 evidence of my earlier findings that in the sperma- 

 togenesis of the common fowl, a large curved 

 chromosome, comparable to the sex-chromosome of 

 other forms, typically passes undivided to one pole 

 of the spindle during the division of the primary 

 spermatocyte. To determine what form this ele- 

 ment assumes in the somatic cells of male and fe- 

 male fowls, a study of the cells of embryo chicks 

 was undertaken. In the main chicks of 10, 13 and 

 20 days of incubation were used. The cells stud- 

 ied were, for the most part, those of the develop- 

 ing nephridial tubules, the nervous system and 

 the gonads. Two fairly well marked curved rods 

 — easily discernible from the other chromosomes — 

 were found to occur with great frequency in the 

 cells of the male. A reexamination of spermato- 

 gonia of both the common and the guinea fowl re- 

 vealed similar paired elements. In the female in a 

 significant percentage of cases only a single ele- 

 ment of like appearance could be found. Thus, 

 for this element, the male appears to be homozy- 

 gous, the female heterozygous. The large curved 

 element of the primary spermatocyte would seem 

 to be in reality, therefore, a double element 

 formed by the fusion of the pair of curved chro- 

 mosomes which exist independently in somatic and 

 early germ-cells. However, the passing over of 

 this element undivided in the first maturation di- 

 vision brings about a condition of dimorphism in 

 the later male germ cells. An important point to 

 be substantiated yet is whether one class of these 

 degenerate without forming spermatozoa, or, if 

 forming them, whether they are not sterile. 



EMBRYOLOGY 



Fish Sy'bridisation an Instrument in MorpJio- 

 genetio Research: H. H. Newman, University of 

 Chicago. 



During the past ten years experiments in fish 

 hybridization have engaged a considerable share 

 of my attention and I have been strongly im- 

 pressed with the possibilities offered by this field 

 of experimentation. Practically any type of 

 morphogenetic disturbance that has been obtained 

 by physical or chemical means is duplicated in 

 some common teleost hybrid. Certain crosses give 

 all of the grades of optic anomaly described by 

 Stockard and others as due to various anesthetics. 

 Double-headed, double- and triple-tailed monsters, 

 etc., are very numerous in some crosses and the 

 genesis of these conditions could be readily stud- 

 ied in living material. 



Among the most interesting anomalous condi- 

 tions seen in these hybrids are the various dis- 

 turbances in the relations of parts of the vitelline 

 and systemic circulation. The heart and its main 

 vessels frequently appear disjoined from the body, 

 and exhibit an independence in differentiation and 

 an automaticity truly striking. Many problems 

 might be cleared up by a study of these conditions. 



The various developmental blocks in hybrid 

 crosses are of considerable general interest, espe- 

 cially to the experimental embryologist. The fact 

 that the end of the cleavage period is the com- 

 monest block to hybrid development is significant 

 in the interpretation of the physiology of cleavage 

 and of gastrulation. 



Other blocks such as those occurring during gas- 

 trulation, especially those involving disturbances 

 of the mechanism of concrescence, are scarcely less 

 significant. 



Apart from hybrid results per se the hybridiza- 

 tion method itself is of much broader application 

 for experimental biology. 



Structure and Function in the Development of the 

 Special Senses in Mammals: H. H. Lane, Uni- 

 versity of Oklahoma. 



By physiological experimentation upon the 

 embryo and fetus of the rat and other mammals 

 at different stages in their development, the time 

 when each of the special senses — touch, equilib- 

 rium, taste, smell, hearing and sight — first becomes 

 functional has been determined within relatively 

 small limits of probable error, and a study made 

 of the corresponding structural development. Con- 

 sidering a reflex are involving any special sense, 

 it has been found that the association centers, the 

 afferent and efferent nerve-trunks, and the effec- 

 tive motor apparatus are all in working order be- 

 fore the special sense organ concerned is capable 

 of functioning, i. e., the organ of special sense is 

 in each case the last link in the chain to be per- 

 fected, and in each case the function is established 

 when (and only so soon as) the proper peripheral 

 sense organ has reached its functional state. The 

 order of development of the organs of special 

 sense and their correlated mechanisms is not that 

 demanded by a Lamarckian hypothesis. It seems 

 evident from these investigations (which are be- 

 ing extended) that the development of the nerv- 

 ous system in general and the differentiation of 

 its constituent parts are due not to epigenesis, but 

 to endogenesis, or predetermination in the oosperm; 

 that these structures appear not as direct responses 

 to the needs of the embryo, but in anticipation of 

 those needs; not under the influence of their spe- 



