CHROMOSOMES OF INDIAN RUNNER DUCK. 34! 



size that it is impossible to pair them. I have placed them in 

 these plates simply to finish the series. In the first spermatocyte 

 cells (Figs. 24-29) these globe-shaped chromosomes are picked 

 out with less difficulty because they are fewer in number; but 

 here the tetrad condition often interferes with distinguishing 

 size relations. However, where a large number of such cells are 

 studied a considerable degree of certainty concerning numbers, 

 morphology, and size relations may be obtained. 



CHROMOSOMES OF THE SPERMATOCYTES. 



The preliminary process of reduction is initiated by syndesis in 

 the course of which the chromosomes become closely associated 

 two by two to form bivalents or gemini. This is, of course, only 

 a pseudo-reduction producing a haploid group of bivalents each 

 representing a pair of chromosomes. Because of this fact we 

 would expect to find in the first spermatocytes where such phe- 

 nomena occur one half the somatic number of chromosomes. 



In counting, the prophase stages were found to be most suit- 

 able. Here the chromosomes lie well apart, which facilitates, 

 not only the counting, but also a study of the forms of each, 

 especially of the large tetrads (Figs. 24-29). Smear preparations 

 were most suitable because whole cells could be used with the 

 resulting certainty that all the chromosomes were present. 

 Metaphase figures were also studied but no drawings of these are 

 here used on account of the tendency of the small tetrads to 

 crowd together in the center of the plate. The large chromo- 

 somes, however, stand out clearly in metaphase and have a 

 tendency to occupy the outside of the circle as in the somatic 

 cells (Figs. 1-22) and as in similar cells of other species (Figs. 35, 



36). 



Figure 24 represents a particularly clear prophase. In Fig. 

 49 the chromosomes of this cell are artificially arranged according 

 to their size. In these bodies the tetrad form can be made out in 

 most of the larger members, and at least the bivalent condition 

 may be seen in the smaller members of the series. This is also 

 true of Figs. 50 to 54. Attention is called to the similarity of the 

 size relations among the members of the spermatocyte series to 

 that of the homologous pairs in the somatic series (Plates 7, 8). 



