88 ASCIDIANS CHAP. 
only Compound Ascidian known from a depth of 1000 fathoms ; 
Polyclinum, Savigny, with a smooth-walled stomach (Fig. 52, 
A); Aplidium, Savigny, with the stomach-wall longitudinally 
folded (Fig. 52, B); Morchelliwm, Giard, with an “ areolated” 
stomach (Fig. 52, D), bearing knobs on the outside; and Amarou- 
cium, Milne-Edwards, in which the ascidiozooid has a long post- 
abdomen and a large atrial languet, and where the stomach-wall 
shows longitudinal ridges breaking up into knobs (pseudo- 
Fic. 52.—Various conditions of stomach in Polyclinidae. A, Polyclinum molle, Herd- 
man; B, Aplidium zostericola, Giard; C, Amaroucium proliferum, M.-Edw. ; 
D, Morchellium argus, M.-EKdw. 
areolated, Fig. 52,C). The last four genera contain many common 
3ritish species. 
Many of the Compound Ascidians die down in winter; but 
amongst Polyclinidae, as in Clavelina, a form of hibernation is 
found, the old ascidiozooids dying, but some of the buds in 
the basal part of the colony accumulating a large store of reserve- 
material in their ectoderm, and lying dormant until spring, when 
they regenerate the colony. 
Group. B. HOLOSOMAT A. 
Body short, compact, with viscera by the side of branchial sac ; 
budding parietal. 
Fam. 6. Botryllidae.— Ascidiozooids grouped in systems 
round common cloacal apertures (Fig. 55). Ascidiozooids having 
the intestine and reproductive organs by the side of the branchial 
sac (Fie. 46, A, p. 82). Dorsal lamina and internal longitudinal 
bars present in the branchial sac. Neural gland, as in Cyn- 
thiidae, dorsal to the ganglion in place of ventral as in the 
majority of Tunicata. The chief genera are—Jotryllus, Gaertn. 
and Pall., with simple stellate systems (Fig. 55), and Botrylloides, 
Milne-Edwards, with elongated or ramified systems. There are 
