Gametogenesis in Cestodes. 
421 
has beeil teased and crushed under a cover glass and examined with an 
oil immersion lens, or the teased preparation has been placed in various 
culture media and studied on a cover glass inverted over a hollow slide. 
The latter method has not been very satisfactory however because of the 
difficulty of focussing with high powers on the very delicate objects 
involved. 
In any cytological study of cestodes, one must be on one’s guard 
against artefacts. Without a careful comparison of living with fixed 
material one cannot be sure that the appearance of the latter is true, and 
even with the use of fresh material as a check, one encounters numerous 
difficulties due to the character of the tissue, and the presence of numerous 
food and chalk bodies. 
The widespread occurrence of the phenomena described in so many 
and varied species however, and the presence of similar conditions in 
living tissue, leads me to believe that they are real and not artificial. 
Observaiions. 
1. Spermatogenesis. 
a) Origin of spermatogonia. 
Relative to the origin of the spermatogonia I have little to add to 
my earlier account. I have however examined the early testes of several 
additional species, thereby verifying my former observations, in so far at 
least as the source of the testis is concerned. They arise in every case 
from appai’ently undifferentiated parenchyma cells, which multiply to form 
little groups of cells surrounded by the testis membrane. The primarily 
unspecialized character of the testis cells is indicated by the presence of 
flame cells in the developing testis of several species, as already recorded 
byme(YouNGl919, b), andis fiirther evidence in support of the contention 
of ChUd (1906, and ’07, 11) that testis cells in Moniezia arise in some cases 
from differentiale d tissue cells. 
Respeeting the method of cell division in the early testes my present 
observations confüni my former conclusions. I have seen several pictures 
strongly suggestive of amitosis and chromidial development and many 
others which are clearly mitotic. It is impossible as Child has already 
pointed out, to prove the occurrence of amitosis in fixed material. The 
skeptic may be shown any number of bi-nucleate cells clearly constricted 
in the middle, or of nuclei in varying stages of constriction, and he vdll 
immediately reply that the former nuclei may have already divided by 
mitosis, cell division lagging somewhat behind nuclear division; while in 
the latter nuclei the constriction may be only temporary, actual division 
Archiv f. Zellforschung. XVII. 28 
