422 
R. T. Young 
being accomplished later by mitosis. I have endeavored to settle the 
question of mitosis or amitosis in cestodes by direct observations on the 
living cells, but thus far without success. Similar failures are recorded 
by Harman (1913) and Morse (1911). For soine reason the cells do not 
grow linder these conditions altho the parenchyma surroimding the testes 
may survive for as miich as forty-eight hours after Isolation, as is eiddenced 
by its motihty on the warm stage. 
Altho I cannot prove the occiirrence of amitosis from my observations, 
I have photographed a suggestive case (fig. 4), leaving it to the reader 
to draw his own conclusions. 
Regarding the possibility of chromidial development in the early 
testes, positive proof is likewise impossible in fixed material. The occur- 
rence of small, spherical, darkly staining particles in the protoplasm of a 
spermatogonium, lying free, or surrounded by delicate membranes, is 
certainly suggestive of some such process, especially when the daughter 
nucleus is found in dose proximity to the parent nucleus. But here again 
proof is impossible unless the actual fomiation of such chromidia cau be 
observed, and even if such formations were occurring in the living cell 
its Observation would be extremely difficult owing to the minuteness of 
the structures involved. The best that can be done is to show the actual 
structures in di’awings and photographs and leave the reader to draw his 
own conclusions (figs. 12, 13, 39 and 41). 
In this Connection an interesting condition is shown in fig. 14, from 
Dipylidium caninum, where the first ceU of a young testis is seen sur- 
rounded by the protoplasm of the parent ceU. It is of course possible that 
these two cells may have arisen by the mitotic division of one original 
progenitor. MTien compared with fig. 12 and 13, 39 and 41, however, it 
is much easier to interpret this cell as arising by endogenous dhnsion, and 
its nucleus from chi'omidia extruded by the parent nucleus. Easier that 
is, if we can free oiirselves from the preconceived idea that all formative 
ceUs (in Metazoa at least) must arise mitotically. 
That mitosis frequently occiu's in the early testis however cannot be 
questioned. It has been observed and figured by Child (1907, II), altho 
according to him it rarely occurs, while Harmax (1913) also mentions 
its rarity at this time. In my earlier study (1913) of Taenia serrata I 
found no mitoses in the spermatogonia, but in those upon which the 
present paper is based I have found it common in the early testes of 
Rhyneobotlirium bulbifer, and occasionally in other worms. IVere the 
Claims for amitosis in cestodes founded solely on the infrequence of mitosis 
they would be quite untenable. 
