152 
R. T. Young 
definite nuclear reticulum but only a fibrillo-granular protoplasm. Con- 
ditions, moreover, vary in different parts of the duct fundament, and in 
different parts of the same worm. Where the fundament approaches 
the surface of the proglottid, bnt before reaehing this, the »nueleolus« 
is scarcely discernible and the entire nucleus very faintly stained; while 
nearer the center of the proglottid. where the duct is older, botli nucleus 
and »nueleolus« are more distinct 1 ). 
There are present liere occasional mitotic figures whose abundance 
varies greatly in nearlv adjoining regions. In one slide I found only 3 
in more tlian a thousand nuclei counted, in another I found 6 or 8 in 
a few hundred. 
In a total of 10 830 2 ) nuclei counted I found one case of apparent 
direct division. It is moreover of interest to note that of 42 probable 
mitoses studied in not one was there any evidence of spindle or attraction 
sphere, and witli six exceptions 3 ) tliey were all prophases. It is evident 
here that direct division will not account for nuclear increase. How then 
can we explain it where mitoses are relatively infrequent? Are we to 
suppose that here there is a resting pcriod in wliich nuclear increase is not 
actively taking place? 1 cannot deny that this is so, and yet it occurs 
in a region of apparently as active growth as that in which mitoses are 
common. An acceptance of mitosis as the sole method of increase in this 
tissue, moreover, will not explain the difference in size (and to some 
extent density) of different »nucleoli«. Furthermore it appears stränge 
that if normal mitosis is occurring actively here, we find so few stages 
beyond the prophase, while the total absence of asters and spindles seems 
inexplicable. I believe rathe? that the prophases, which occur liere in 
some places commonly, are to be regarded as remnants of a degenerating 
process, while the actual nuclear increase is taking place de novo. 
An examination of several nuclei shows some in which a complete 
membrane is evidently lacking. but in others it appears to be complete. 
We come now to a consideration of another family of Cestodes, the 
Phyllobothriidae, and as an example of this group we will take 
Crossobothrium laciniatum. 
(Figs. 11 and 12.) 
In sections of this worm from the neck region I find a considerable 
massing of nuclei about the central part of the proglottid. In these nuclei 
I refer liere to the average duct, individual variations of course occur. 
2 ) See footnote 1). p. 145. 
3 ) One of these was a metaphase (mother star). Iainuncertainastotheotherfive. 
