432 
R. T. Youiij 
pretation as polar bodies highly improbable. Apait from such structures 
and the yolk cells already mentioned I find no evidence of polar bodis in 
any of the nunierous species of cestodes studied by me. 
3. Cleavage. 
To this process, which follows, but is not a part of gametogenesis, 
I have paid comparatively little attention in this study, and hence have 
little to add to my own previous account and those of other authors. 
There is no question but that mitosis frequently occurs in the early embryo, 
and is perhaps sufficient to account for all cell multiplication. In my 
previous paper (1. c.) I have shown several cases^) which I described 
either as amitosis or chromidial nuclear development, and I still incline 
to my first interpretation. I well recognize however the difficulty, if not 
impossibility, of absolute proof of this hypothesis, without the observation 
of the process of cell division in living material. 
Discussion of results. 
There are nunierous accounts of amitosis in both plants and animals, 
and these accounts are not limited to differentiated somatic cells, but 
include embryonic and even germ cells as well. An extensive list of 
references to the subject has been given by Conklin (1917) in his paper 
on “Mitosis and amitosis”, and hence need not be repeated here. Never- 
theless these accounts have met with general skepticism on the part of 
biologists, so that while it is generally conceded that amitosis may occur 
in highly specialized ceUs, or under abnormal conditions, it is not admitted 
by most biologists that it ever occiu’s normally in undifferentiated tissue 
and least of all in germ cells. Science is rightly skeptical regarding new 
discoveries, and all such must have ample proof before they can be accepted. 
Claims for amitosis have been founded, so far as I am aware, exclusively 
on fixed material, and as various writers have pointed out, these Claims 
admit of entirely different interpretations. Until amitosis is actually 
seen in living tissue it will remain a theory and not a fact. 
The difficulty of proving amitosis in germinal tissue is not however 
sufficient reason for overlooking all cell phenomena which do not readily 
fall in line with generally accepted belief. To do so is but to follow the 
example of the early naturalists, who, upon discovering some specimen 
which did not correspond to any established species, merely tlnew it away 
as a freak, unworthy of consideration. The fact that cestodes are degene- 
1) See figs. 82, 88 and 91. 
