No.398. WILLEY ON THE ENTEROPNEUSTA. 125 
posterior part of the dorsal surface of the proboscis stalk, as in 
other species, but ** into the base of the medullary tube, some- 
what behind the anterior neuropore.”’ 
* By a legitimate mental abstraction" Dr. Willey derives 
from this fact a “theory, as to the broad truth of which” he 
is himself “quite convinced," and which he states in these 
words: * The proboscis pore of the Enteropneusta is repre- 
sented by and is homologous with the inner or cerebral open- 
ing of the neuro-hypophysial apparatus of the ascidian larva ; 
the end sac of the Enteropneusta typically communicates inter- 
nally with the ccelom, but within the limits of the group we 
find signs of its emancipation from the ccelom ; the hypophysial 
canal of the ascidian larva has no relations with the body cavity, 
but it opens at one end into the medullary tube (cerebral vesi- 
cle) and at the other into the branchial sac at the base of the 
buccal cavity. Thus a special significance is given to the 
peculiar mode of origin of the ascidian subneural apparatus 
(gland and duct), and an explanation is forthcoming as to the 
apparent absence of anything like a proboscis pore in the ascid- 
ian larva.” This adds another and startling hypothesis to the 
several that have been advanced as to the homologies of the 
ascidian neural gland. Allow me to refer for a moment to 
these. 
Masterman's recent attempt to homologize the so-called noto- 
chordal pouch of the Hemichordata with the ascidian neural 
gland seems to imply a failure to understand the real nature of 
the latter organ. The notochordal pouch, so far as we can 
judge, is endodermal, a derivative of the pharynx. The neural 
gland of ascidians! is derived from the central nervous sys- 
tem, its duct is the anterior end of the central neural tube, and 
its aperture is usually regarded as the neuropore. The neural 
gland has no known relation to the endoderm, except that it 
opens into a portion of the pharynx which may be of endoder- 
mal origin, but which there is some reason to believe may be 
derived from the stomodzeum. 
1 I say the neural gland of ascidians rather than of Tunicata, because the neu- 
tal gland of certain tunicates, the Salpide, is of such a peculiar nature that it is 
difficult to compare it with that of the ascidians. 
* 
