of Edinhtrgli, Session 1882-83. 
145 
4. On the Homology of the Neural Gland in the Tunicata 
with the Hypophysis Cerebri. By W. A. Herdman, 
D.Sc., F.L.S.^ Professor of Natural History in University 
College, Liverpool. 
{Ahstract.) 
In an ordinary simple Ascidian, where both the branchial and 
atrial apertures are at or near the anterior extremity of the body, 
the region lying between them — the interoscular area of Lacaze- 
Diithiers —is small in extent, and contains three important structures, 
the nerve ganglion, the neural gland, and the dorsal tubercle, lying 
close together. The ganglion in such a case is elongated dorso- 
ventrally, and gives off nerves at its two extremities, one set 
ventrally and anteriorly towards the branchial aperture, and the 
other set dorsally and posteriorly towards the atrial. 
In those species, however, in which the atrial aperture is near or at 
the posterior end of the body, the interoscular area is large, and forms 
the dorsal edge of the body. The nerve ganglion may remain ante- 
lior in position, or it may be placed far back so as to be nearer to the 
atrial. In this case, the nerves given off from the extremities of 
'he ganglion run, the one set anteriorly and the 'other posteriorly. 
Wherever the ganglion may be, the neural gland is always found 
in close relation to it, either upon its posterior or ventral surface, 
according to the direction in which the long axis of the ganglion is 
placed. This neural gland consists of a mass of more or less ramified 
csecal tubules imbedded in connective tissue, and all springing from 
a central space or wider tube which underlies the ganglion. The 
presence of tliis organ was first distinctly pointed out by Albany 
Hancock in 1868,* but this able investigator does not seem to have 
assigned any function to it. 
The mysterious dorsal or “ olfactory’’ tubercle was first described by 
Savigny in 1816, under the name of “ tubercule anterieur.” Since then 
it has been discussed by almost all who have worked at the Tunicata ; 
it has received many names, but has usually been regarded as some 
sort of olfactory organ. It is invariably placed at the anterior end of 
the branchial sac, posterior to the circle of tentacles, and usually in a 
* “On the Anatomy and Physiology of the Tunicata,” Jour. Linn. Soc. 
Zool., vol. ix. p. 335. 
