The Somatic Nuclei of Certain Cestodes. 
161 
that these apparently immature nuclei are not actually so but are rather 
degenerate, having in one case, lost their chromatin content (represented 
by those in which the membrane alone is present), and in the other, hav- 
ing lost their membrane and most of the chromatin, a single small 
»nucleolus « alone persisting. It is very improbable, however, that in re- 
gions of actively growing tissue (such as is represented by those parts 
from which most of the sections under discussion were cut) anv con- 
siderable number of nuclei should be undergoing degeneration. 
That mitosis may degenerate has been suggested by Calkins (1901) 
in the case of the Infusoria, tho what evidence there is here that the 
process is retrogressing rather than progressing is not clear. 
The existence of a definite and complete nuclear membrane, dis- 
tinct from the nuclear reticulum is still an open question. My observations 
tend to show that in Cestodes a such membrane usually does not exist. 
A full discussion of the bearing of these facts on the question of the 
part played by the nucleus in the transmission of hereditary qualities 
may be found in my paper (1. c., p. 242), and in those of Child (1904: 
p. 557 and 1907c: p. 293), and need not be repeated here. I wish to call 
attention, however, to the surmise of the latter (1907d: pp. 169 — 79, 1907e: 
pp. 289 — 93) that the type of cell division depends upon »the relation 
between the Stimulus to growth and the intake of material« (1. c., p. 171), 
amitotic division tending to occur where the »nucleus is forced far from 
a condition of equilibrium« (1. c., p. 171) between the two above factors. 
With this hypothesis it is difficult to explain the conditions found in 
Anoplocephala sp., where in certain parts of the developing genital ducts 
mitotic prophases were common, while in other, not far distant regions, 
they were comparatively very rare. It is difficult to understand why 
that here in two nearly adjoining regions of the same tissue, and appar- 
ently under the same conditions, there should be in one case »equi- 
librium between intake of material and functional transformation« 
(1. c., p. 171) and in the other not. The more common occurrence of 
mitosis in the developing sex cells than in other tissues of Cestodes is 
I believe more readily explained by the Suggestion which I have given 
above (pp. 158 — 159) than by Child’s hypothesis. 
It is to be lioped that further investigation will throw more Mght 
on the significance of the nucleus, and on its methods of multiplication 
in the Cestodes. 
In conclusion I wish to thank Prof. Edwin Linton and the Zoolog- 
ical Laboratory of the U. S. Bureau of Animal Industry for their cour- 
tesy in the identification of material. 
Archiv f. Zellforschung 1 . VI. 
11 
