ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 385 
as myself, to have endeavoured to trace the fate of the ovisac and of 
its epithelium. And yet, with the development of Pyrosoma before 
me, it is impossible to arrive at a conclusion in the absence of infor- 
mation on this head. The long retention of the foetus of Sa/pa in 
connexion with the parent and nourished by its blood, in contrast 
to the early separation of the foetus of Pyrosoma and the turning of 
its cyathozooid to account in another way, leads me to conceive that 
considerable differences will be found in the details of their develop- 
ment, though I suspect further inquiry will prove that, in essentials, 
they are very similar. 
EXPLANATION OF THE PLATES. 
PLATES NNX. [PLATE 29] AND NXNI. [PLATE 30.] 
The following letters and figures have the same signification throughout. 
a, the test ; at, its oral ; a”, its cloacal fibrillated layer; a°, labial processes of the ascidio- 
zooids ; a4, lip or so-called sphincter of the cloacal aperture ; a°, cells of the embryonic 
test. 
4, outer tunic. 
c, inner tunic, or intestinal wall. 
d, atrial tunic. 
e, oral aperture. 
f, tentacular membrane ; £1, hzemal tentacle. 
g, é! anterior muscles ; g®, posterior or atrial muscles. 
A, peripharyngeal ridge. 
z, endostyle. 
7, epipharyngeal folds. 
k, hypopharyngeal band and sinus ; 21, languets ; 2°, diapharyngeal band. 
7, branchial sac ; 71, horizontal branchial bars ; 2°, perpendicular branchial bars ; 7%, stigmata. 
m, alimentary canal; 7', cesophageal aperture ; 7%, cesophagus ; 73 stomach ; 4, intestine. 
2, tubular organ, probably hepatic. 
0, anus. 
é, mid-atrium ; 21, lateral atria ; A’, atrial aperture. 
r, heart ; 71, sinuses; 72, stolons of the adult ascidiarium ; 7%, vascular bands, connecting the 
branchial sac with the parietal sinus; 74, stolons of the embryonic ascidiarium, or 
tetrazooid. 
5, ovisac ; s', its duct ; s®, lining of the ovisac. 
t, testis ; 21, vas deferens ; /?, spermatozoa. 
a, yelk ; 2! germinal vesicle ; «® germinal spot ; #°, contents of the germinal vesicle. 
w, bud; w?, its peduncle. 
x, alimentary or trophic blastema of the nascent bud; «1, its generative blastema; <x”, its 
tegumentary blastema. 
y, the circular cellular patch, probably a renal organ. 
2, the ganglion ; 2!, nerves ; 3°, the ciliated sac ; 23, the tubercle. 
@, elzeoblast. 
en, embryonic endoplasts within the germinal vesicle. 
42. blastoderm. 
cl, cloaca. 
VOL. II CG 
