314 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATORY. 



not increased in size. A like change in the ordinary dyads 

 now shows granules in their synaptic ends staining similarly 

 to those previously noted in the spermatogonial chromosomes. 

 (See fig. 29.) 



SECOND SPERMATOCYTE. 



The ordinary dyads in a prophase of the second spermato- 

 cyte resemble those in figure 28. The condition of the acces- 

 sory was not noted. Division proceeds in the usual manner, 

 resulting in the separation of single chromatids (figs. 30-32). 

 Figure 33 shows a cell formed by this latter division. Diffu- 

 sion of the chromatids has taken place within the nucleus. 

 Persisting bodies of chromatin are noted distributed' irregu- 

 larly through the less concentrated nuclear substance. A 

 round, deeply staining mass of spindle fibers is observed ad- 

 joining the nucleus (fig. 33 a). After the stage represented 

 in figure 33 we obtain figure 34, a late stage in the developing 

 spermatid. All traces of material staining like condensed 

 chromatin have disappeared with the exception of the middle 

 piece (fig. 34 a). It is uncertain whether this body lies within 

 or without the membrane b. 



CONCLUSIONS. 

 In conclusion, I wish briefly to summarize and correlate the 

 history of the unusual chromosomal elements noted in the four 

 generations of germ-cells just described. I have already re- 

 ferred to those occurring in the spermatogonial chromosomes 

 as the polar granules. There their prominence and constancy 

 claim for them recognition as important elements in the or- 

 ganization of the individual chromosomes. By a consideration 

 and comparison of figures 4, 6 and 9 it is plain that the position 

 of these granules coincides with the proximal ends of the 

 chromosomes, and evidently, from figure 6 — which shows that 

 the granules occupy that point of the chromosome which is 

 nearest the pole — mark the point of attachment of the spindle 

 fiber. If now we can prove that these granules maintain the 

 same position with respect to the remaining portion of the 

 chromosomal substance throughout its life-history, and also 

 that every such granule is the direct descendant of a preceding 

 granule exactly like it in form and position, we may, I think, 

 safely conclude that every chromosome is definitely and un- 

 changeably polarized and that the point of spindle fiber at- 



