326 
THE VOYAGE OF H.M.S. CHALLENGER. 
A distinct abdomen is present in the Ascidiozooid only in the genus Thylaciwm, 
Cams, so far as is known. In all other members of the family the alimentary canal 
lies alongside the branchial sac as it does in the Botryllidse and in most of the Simple 
Ascidians. In some cases {e.g., Synstyela incrustans) the test may be prolonged beyond 
the Ascidiozooids to form a spreading margin to the colony, in which numerous vessels 
ramify and terminate in dilated bulbs. It is probably in connection with these terminal 
bulbs that young Ascidiozooids are formed. 
The branchial sac is always large. When longitudinal folds are present {e.g., 
Goodsiria placenta) they are in the rudimentary condition^ so frequently found amongst 
the Styelinse. In some cases {e.g., Goodsiria coccinea) there are no folds in the branchial 
sac. Dorsal languets are never present in the family. 
The reproductive organs are present on both sides of the body in the form of 
little “ poly carps ” or masses of ovaria and spermaria partly imbedded in the mantle, 
and projecting into the peribranchial cavity just as in the species of Polycarpa. The 
curious “ endocarps ” of unknown function, which have previously only been known from 
the Styelinse, are also present on the mantle of some if not all species of the Polystyelidse 
{e.g., Synstyela incrustans, see PI. XLVI. fig. 14). In some cases the polycarps are 
hermaphrodite {e.g., Goodsiria placenta), as they are in the Simple Ascidians, while in 
other cases they are unisexual {e.g., Goodsiria pedunculata and Synstyela incrustans, 
PL XLVI. figs. 12, 13), and the male and female poly carps differ somewhat in appearance. 
The genera ^ which belong to this family may be distinguished by the following 
characters : — 
POLYSTYELID^. 
Ascidiozooids projecting 
above the general surface 
of the colony. 
Abdomen as No abdomen 
long as the present, 
thorax. . | 
I Polystyela. 
Tliylacium. 
Colony consisting 
of a number of 
small masses 
connected by 
creeping stolons. 
I 
Chorizocormus. 
Ascidiozooids completely 
imbedded in the 
common test. 
Colony thick 
and 
massive. 
Colony thin 
and 
incrusting. 
Test incrusted 
with sand. 
1 
Oculinaria. 
j Synstyela. 
Test not 
incrusted with 
sand. 
I 
Goodsiria. 
* See Herdman, On Individual Variation in Simple Ascidians, Trans. Lit. and Phil. Soc. of Liverpool, vol. for 1882. 
2 It is possible that the genus Pyura, founded by Blainville for an animal discovered by Molina (Saggio sulla 
Storia naturale del Chili, I782),’'and since found by Cunningham (Notes on the Natural History of the Strait of 
Magellan, Edinburgh, 1871, p. 430) on the shores of the Bay of Arauco, and described as being a “ Social Ascidian,” 
belongs to this family. But the little that is known of its structure is not sufficient to determine its position with any 
certainty. 
