60 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



be demonstrated only by counting, owing to the fact that the difference 

 in size between the specialized element and the other chromosomes is too 

 small to serve in identification. However, the chromosomes are so distinct 

 that accurate enumerations can be readily made (Plate 6, Figs. 77, 78). 

 In later stages of the early spermatid, the accessory chromosome again 

 becomes for a time morphologically distinguishable by means of the 

 same characteristic by which we were able to identify it during the sper- 

 matocyte changes, i. e. its retention of the homogeneous condition at the 

 time when the other chromosomes have again resumed their granular 

 appearance. However, this does not long serve as a means of identifica- 

 tion, for at the beginning of the condensation of the nucleus of the sper- 

 matid into the head of the spermatozoon the accessory chromosome again 

 becomes indistinguishable. The appearance and relations of the various 

 parts to each other during the telophase of the last spermatocyte division 

 are shown in Figure 77. The centrosome, one in each of the two pro- 

 spective spermatids, lies at the pole of the cell opposite the remnants of 

 the spindle. It consists of a simple spherical granule, around which 

 there is no indication of a centrosphere ; however, faint asti-al radiations 

 in process of disintegration are still to be seen. It lies in close contact 

 with the cell membrane ; in fact, at this and slightly later stages it seems 

 to cause a distinct outward bulging of the membrane at the point of 

 contact (Figs. 77, 79). 



The chromosomes, either sixteen (Fig. 77) or seventeen (Fig. 78) in 

 number, lie in a clear area or vacuole situated at a point about four times 

 as far from the Zwischenkorper as from the centrosome (Figs. 77, 78). 

 They are at first small homogeneous bodies, but soon become apparently 

 larger owing to the more diffuse condition of the chromatin (Figs. 78, 79). 

 This change is accompanied by the formation of a nuclear membrane, 

 winch appears first at about the stage represented in Figure 78. This, 

 while thin and delicate, is very distinct by reason of the definite black or 

 gray stain which it takes, while the cytoplasmic reticulum assumes an 

 orange-red color in preparations stained with Heidenhain's iron-haema- 

 toxylin and Congo red. 



The cytoplasmic reticulum of the young spermatids has the same 

 close-meshed, deeply stained condition which we have already noticed to 

 be characteristic of the same material during the early stages of the 

 spermatocyte mitoses. This, as in the former cases, is due to the fact 

 that the archoplasm taking part in the preceding division has been 

 broken down and is now distributed throughout the entire cytoplasm. 

 As we shall soon see, aggregations of archoplasm are later to be met with 



