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Proceedings of the Royal Society 
additional species, and enunciated tlie theory suggested to him by 
E. van Beneden, that the neural gland was renal in function, and 
was the hornologue of the hypophysis cerebri of the vertebrate 
brain. In favour of this homology ma}’' be considered — 
1. The position of the gland upon the ventral surface of the 
nerve centre and above the pharynx. 
2. Its glandular nature. 
3. Its connection with the anterior end of the pharynx by a duct — 
Balfour, Kolliker, and others having shown that the hypophysis or 
pituitary gland in higher vertebrates arises as a dorsal diverticulum 
from the stomodseum, but afterwards loses this connection. 
From my own observations on a number of different forms of the 
Tunicata, I can confirm Ussow and Julin’s statements as to the 
presence of a duct from the neural gland and its connection with the 
slit of the dorsal tubercle, and, like Julin, I am unable to find any 
nerve supplying the supposed sense organ. I have, however, in 
several cases seen certain of the epithelial cells covering the edges 
of the slit which had a striking resemblance to sense cells, such 
as those in the ectoderm of Adinice. This observation taken along 
with Julin’s descriptions, and especially with the condition of affairs 
in some specimens of Ascidia mammillata which I have recently ex- 
amined, has suggested to me that possibly the dorsal tubercle may be 
both the aperture of a gland corresponding to the hypophysis cerebri, 
and also a sense organ, probably of an olfactory or gustatory nature. 
Ascidia mammillata is one of the forms discussed by Julin in his 
second paper. It is a large species, with the branchial and atrial 
apertures rather far apart, and the ganglion at a considerable distance 
from the anterior end of the body, the interoscular area being of 
large extent. Julin found that the neural gland in this species did 
not form the usual compact mass, but was in a somewhat rudi- 
mentary condition, and that besides having the usual duct running 
anteriorly to communicate with the pharynx by the dorsal tubercle, 
it had also a number of short funnel-shaped apertures into the peri- 
branchial or atrial cavity enclosed by the mantle ; so that in this 
species the products of the neural gland might be excreted either 
into the branchial sac by the main duct and dorsal tubercle, or 
into the dorsal part of the peribranchial cavity by the lateral shorter 
duct^ This peribranchial cavity communicates directly with the 
exterior by means of the atrial aperture, and is the cloacal cavity 
