480 
of the commencing diverticulum of the digestive tract and extending 
slightly down on the left side of the vesicle. These cells constitute 
the rudiment of the sexual organs, and are derived in the same 
way as are the pericardium and dorsal tube, namely by proliferation 
of cells in the wall of the inner vesicle. Fig. 5 (s. r.,) illustrates the 
origin of the rudiment which at this young stage is an irregular mass 
of cytoplasm containing a few scattered nuclei; the interruption in the 
outer membrane of the wall is clearly shown. There is the same 
evidence again as was pointed out above, that cells of the blood 
become attached to the rudiment and contribute to its formation. 
The rudiment lies at first in the angle made by the base of the 
digestive tract and the side of the vesicle, but after it has become 
detached from the latter, it is carried further down on the left side 
apparently by the growth of the gut, in the bend of which it seems 
to be loosely held for some time. As far as I have followed it, the further 
development of the sexual organs takes place in the manner described 
by Van BenepEN and Juin (1. c.) for Perophora Listeri. 
The rudiment soon becomes a spherical vesicle by the appearance of 
a cavity in its centre, and the genital cord grows out from it anteriorly 
as a long string of cells. This simple vesicle divides into two whose 
cavities at first communicate but finally become separated. One of 
these vesicles gives rise to the ovary, the other to the testis, and the 
genital cord which splits into two ducts, forms the oviduct and vas 
deferens. 
Concluding remarks. 
From the above brief account it is seen that the bud-development 
of Ecteinascidia is strikingly like that of Perophora, of P' 
annectens in particular, and although the peculiar rotation or 
transverse shifting of the inner vesicle which occurs in the latter 
genus and complicates the development, is absent in the former, the 
manner in which the important organs are formed, is very much the 
same. The absence of an epicardium with which the formation of the 
pericardium is closely connected, sharply contrasts these two genera 
with Clavelina, which presents practically a different method of 
development. 
In Ecteinascidia and Perophora annectens the peri- 
cardium, dorsal tube and ganglion, and in the former spccies the 
sexual organs also, are all formed, for the greater part at any rate, 
from cells which wander out directly from the wall of the inner vesicle 
into the rudiments, and it is quite probable as we have seen, that 
