88 NICHOLS — SPERMATOGENESIS ONISCUS ASELLUS LINN. [April 4, 



togonic divisions (Fig. 15). In Fig. 61, a stage intermediate 

 between 58 and 62, some of the chromosomes likewise appear of 

 greater length than others. It might be supposed that the longer 

 ones represent the side view, the shorter ones the end view, of the 

 chromosomes. This need not, however, necessarily be the case, 

 for the chromosomes vary amongst themselves in size (Fig. 58 and 

 previous figures). It is possible, too, that in some cases the chro- 

 mosomes are seen slightly foreshortened and that their true dimen- 

 sions do not appear in the figure. I feel it, therefore, impossible 

 to ascertain with the desired degree of certainty the plane of the 

 second spermatocytic division. 



In the late anaphase (Fig. 66) the chromosomes are more or less 

 indistinguishably massed together. On each of the interzonal 

 fibres in the equator is a minute swelling. These become reduced 

 in number (Fig. 67).^ 



4. Metamorphosis of the Spermatids. 



The chromosomes spread apart, a nuclear membrane is developed 

 and the daughter cells become the spermatids. The gradual con- 

 version of the chromosomes into a fine reticulum is illustrated in 

 Figs. 69 and 70. 



The nucleus now commences to elongate at one end (Fig. 72), 

 and this continues until the entire nucleus is transformed into a 

 shape somewhat like that of a narrow flask (Fig. 74). The nuclear 

 network is extremely delicate and takes the iron hsematoxylin stain 

 more faintly than previously. In cross section (Fig. 74^^; numer- 

 ous fine dots appear interspersed with clear areas (vacuoles). This 

 vacuolated appearance is sometimes evident at an earlier stage 

 (Fig. 71). 



During the transformation of the nuclei the cell boundaries have 

 entirely disappeared and the nuclei lie in a common mass of cyto- 

 plasm. Several of them become associated together, and their 

 extremities, elongated into slender threads, are surrounded by a 

 clear, homogeneous, well-defined area of cytoplasm, while the 

 more or less contorted bodies of the nuclei still lie in an undefined 

 mass of cytoplasm (Fig. 77^). 



A cytoplasmic thread of extreme delicacy can be traced from the 



^ During the examination of the foregoing stages I have seen nothing similar 

 to the accessory chromosome (chromatin nucleolus) of insects, as described by 

 Montgomery (1898) and Paulmier (1899). 



