212 PIT TER. iVon. X11, 
a physiological explanation somewhat similar to that above 
supported as the cause of the course of things in the Ascidian 
bud. I refer to the ectodermal origin of the bud in Rathkea 
octopunctata, as recently described by Chun (95). The buds of 
this medusa develop on the manubrium, and on that portion of 
it in which the endoderm cells, as is clearly shown by the 
author’s description and figures, are highly modified for the 
digestive function. On the other hand, the ectoderm cells are 
as clearly much less highly modified. When we look for a 
reason why the ectoderm retains to so considerable a degree 
its undifferentiated character, we find a sufficient one in the 
fact that it is largely relieved of the protective function that 
usually belongs to this layer in adult animals by its being itself 
well protected by the deep, close sub-umbrella of this medusa. 
And in the two facts that the buds arise in a region where the 
endoderm is highly modified for the digestive function, and 
that the ectoderm remains comparatively unmodified, appear, 
as I believe, an adequate reason why the ectoderm alone 
contributes to the formation of the buds. 
Braem (95), in puzzling over this case, suggests that the 
most probable explanation of the anomalous condition is to be 
found in the fact that the buds arise from the same layer, and 
not remote from the position where the sexual cells are pro- 
duced.. _But—Chun states, page 32> that “Mann trifft keine 
Sporen oder parthenogenetischen Eizellen an, welche durch 
Grosse und abweichendes Verhalten des Inhaltes sich von den 
ibrigen Ektodermzellen abheben.”’ 
Of course, if my explanation of this case is correct, we may 
expect to find other instances where similar conditions and 
causes will have produced like results ; as, for example, in the 
budding medusa of Bougainvillia Niobe recently described by 
Mayer (94), which is likewise a deep-belled form, and in which 
the buds “spring from the gastric region manubrium.” But I 
do not think that if in a particular instance, where the condi- 
tions are right to produce the results, they still do not appear, 
we should on that account be justified in concluding their 
inefficiency to produce them. It is highly probable that, in 
groups of animals which reproduce by budding, the faculty is 
