Young, Cytology of Cestoda. 307 



typical nuclei, with nuclear membranes enclosing chromatin 

 granules or so-called „nucleoli", while others consist entirely 

 of a homogeneous, densely stained mass. In some cases this latter 

 appearance is probably due merely to shrinkage. That such an 

 explanation applies to all or most of these cases is rendered im- 

 probable by micro-chemical tests, in which chromatin solvents 

 remove from these darkly staining cells their staining capacity; 

 and further by cases in which a long extraction of the stain fails 

 to reveal any sign of a differentiated nucleus. For this and further 

 evidence elsewhere cited (Young 1908, 1910) I believe these 

 darkly staining or atypical cells to contain nuclear matter diffused 

 thruout the cell body. 



Not only in nuclear development, but also in other cyto- 

 logical processes, notably those of gametogenesis, do cestodes 

 show degeneracy. In spermatogenesis groups of a few cells are 

 found in the parenchyma, in which nuclei are arising in 

 part by a very primitive sort of amitosis and in part from chromatin 

 granules, either extruded by pre-existent nuclei, or arising de 

 novo in the cytoplasm. Soon the nuclei develop typical loose 

 skeins, but mitosis apparently does not proceed further than this, 

 for in examining a large number of testes I have found only 

 one possible instance of later stages. The sperma- 

 togonia now fuse to form a syncitium, the skeins break up and 

 the chromatin particles resulting therefrom are scattered thru the 

 former. More numerous and much smaller Ridimentary nuclei 

 mow appear thruout the syncitium, whether arising de novo or 

 from the skein remnants is impossible to say. These latter nuclei 

 appear to play no part in spermatogenesis, but are destined to 

 early degeneration. The sperms mean while develop directly from 

 the protoplasm of the syncitium, arising at first peripherally and 

 developing centripetally most of the mass being consumed in 

 their production. Many of the sperms, if not all, arise as tubes 

 rather than threads, becoming later Condensed into the latter, 

 such condensation usually appearing first at one point on the 

 periphery. 



The ovaries arise as a branching follicular network in which 

 nuclear development is progressing similarly to that in the early 

 testes. With the growth of the ova their nuclei develop skeins which 

 soon revert to the resting condition without showing any further 

 mitotic stages. The ovarian nucleus at this stage appears as a 

 large Space traversed by a chromatin reticulum, and surrounded by 

 an incomplete but distinct membrane apparentlv derived from the 

 latter. 



The ova now pass into the oviducts and undergo an abortive 

 maturation mitosis. The beginning of the latter is marked by 

 the appearance of asters on the border of the nucleus. The so- 

 called centrosome possessed by these is nothing I believe other 



