No.1.]} BUDDING IN GOODSIRIA AND PEROPHORA. 209 
this has occurred most conspicuously it has been before the 
appearance of the ganglionic thickening in the dorsal wall. It 
is possible that this may be an embryonic trace of the glandular 
portion of the hypophysis that is so well developed in some 
Ascidians. There is no particular evidence for this, but the 
fact that this structure is known to undergo degeneration in 
some Ascidians gives the suggestion some probability. 
In my description of Perophora annectens (94) I have 
called attention to the fact that the posterior ends of the 
ganglion and duct are not situated in the median plane of the 
body, but are considerably to one side. This condition is 
assumed early in the development of the organs, and is almost 
always quite pronounced, but I do not see that it has any par- 
ticular significance. 
C. GENERAL CONCLUSIONS AND REFLECTIONS. 
1. APPLICATION OF GENERAL DEVELOPMENTAL PRINCIPLES 
TO AN INTERPRETATION OF THE FACTs. 
It being now, as I believe, fully established that the nervous 
system of the Ascidian bud has a different origin from that of 
the embryo, we must seek for an explanation for so anomalous 
a fact, —for the processes of evolution are of more importance 
from a scientific point of view than are their particular products. 
The explanation, which I think to be the true one, has already 
been pointed out, first by Seeliger (85), and more recently by 
Hjort (95). The latter, in particular, has dwelt quite fully 
upon the point. It is, however, a matter of such importance 
that I believe it deserves to be emphasized still further. This 
is an instance where nature herself has performed an experi- 
ment in modifying the ordinary course of development. The 
revolutionary and comparatively crude, but still, in consider- 
able degree, successful efforts of experimental embryologists to 
artificially divert cells that would normally become ectoderm 
into entoderm, or structures ordinarily of endodermic origin, 
have been deservedly held to be of the highest moment for 
solving the fundamental problems of animal development. Cer- 
