52 ASCIDIANS CHAP. 
All the blood-spaces and lacunae are probably derived, like 
the cavity of the heart, from the blastocoel of the embryo, and 
are not, like the cavity of the pericardium, a part of the coelom 
(of endodermal origin). 
Neural Gland and Dorsal Tubercle.—In the dorsal median 
line near the anterior end of the body, and imbedded. in the 
mantle on the ventral’ surface of the nerve-ganglion, there lies a 
small glandular mass—the neural gland—which, as Julin first 
--- test 
------- mantle 
re Peribranchial 
. cavity 
Bi a p.br 
"EB EOE 
ae d.bl.s 
Branchial sac 
B 
Fria. 24.—Antero-dorsal part of Ascidia showing the relations of the layers of the body, 
and of the nervous system. A, in sagittal section ; B, in transverse section. d./.s, 
Dorsal blood-sinus ; d./, dorsal lamina; d.n, dorsal nerve; d.¢, dorsal tubercle ; 
ect, ectoderm ; en, endoderm ; e.p.br, epithelium of peribranchial cavity ; g/.d, duct 
of subneural gland ; 7.v points to the ciliated epithelium covering a longitudinal 
vessel of branchial sac; m, mantle; m, nerve; .g, ganglion ; .g/, neural gland ; 
p.br, peribranchial cavity ; pp.b, peripharyngeal bands ; sph, branchial sphincter ; 
t, t’, test ; tn, tentacle. 
showed, there is some reason to regard as the homologue of the 
hypophysis cerebri of the Vertebrate brain. Metcalf has recently 
shown that the neural gland may be a double structure—partly 
cerebral and partly stomodaeal—as in Vertebrates. 
The function of this gland is still somewhat mysterious. It 
may merely form the viscid secretion which is carried along the 
peripharyngeal bands and down the dorsal lamina. On the other 
hand, it has been suggested that the function of the organ may 
possibly be renal, for the removal of nitrogenous waste matters in 
the neighbourhood of the nervous system. Finally, it may be a 
lymph gland. 
1 Except in Cynthiidae and Botryllidae where it is dorsal. 
