EEPOET ON THE TUNICATA. 
163 
Ascidiozooid is female and the older one male, and the ova and spermatozoa develop from 
mesodermal cells in the same reproductive tubules, which, however, become more numerous 
and change their shape somewhat when being converted into spermatic vesicles. The 
vas deferens is very long and convoluted, and is conspicuous from near the top of the 
post-abdomen onwards. It adheres to the rectum along its entire length, and terminates 
a short distance in front of the anus. 
This species is particularly interesting on account of the resemblances it shows to 
some of the Ascidiae Simplices. From its general anatomy, and especially from the 
relations of the intestine to the branchial sac and the reproductive organs, it is clearly a 
member of the family Polyclinidae, but the musculature of the mantle is quite unlike that 
of most Compound Ascidians. The muscle bands in the thoracic region, while branching 
and anastomosing irregularly, have their main lines more or less antero-posterior (PI. 
XXII. fig. 4), while the general rule amongst Compound Ascidians is that the chief 
muscle bands should run transversely. Then the branchial sac shows resemblances to 
the Clavelinidse in the large number of stigmata, in the presence of the rudimentary 
connecting ducts on the transverse vessels, and in the long, narrow languets. Lastly, 
the tentacles are numerous and closely placed at their bases (PI. XXII. fig. 13), just as 
in many Ascidise Simplices, while in Compound Ascidians, as a rule, the tentacles are 
few in number (usually eight or sixteen), and are arranged regularly at equal distances 
apart. 
Atopogaster} n. gen. 
Colony massive, and usually of large size. 
Systems simple or inconspicuous. 
Ascidiozooids large or small, always much elongated antero-posteriorly. Branchial 
aperture six-lobed. 
Test thick, and usually cartilaginous and tough; not incrusted with sand. 
Branchial Sac usually well developed. 
Alimentary Canal large. Stomach-wall folded transversely. 
Post- Abdomen long. 
I have separated this little group of species from the other Polyclinidse on account of 
their possessing a large stomach, the wall of which is thrown into transverse folds. It 
is very convenient to make use of the characters of the stomach-wall in dividing up this 
family into sections, a course pursued first by Giard ; but I am doubtful whether the 
groups so produced are in all cases natural. In the present genus the mere presence of 
folds distinguishes from Synoicum, Morchellium, Morchellioides, and Sidnyum, while 
^ From oiroTTo; and yxar'/i^. 
