88 ASCIDIANS 



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) ; Morchellium, Giard, with an "areolated" 

 stomach (Fig. 52, D), bearing knobs ou 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- 



A B 



FIG. 52. Various conditions of stomach in Polyclinidae. A, Polydinum molle, Herd- 

 man ; B, Aplidium zostericola, Giard ; C, Amarouciuin proliferum, M.-Edw. ; 

 D, Morchellium argus, M.-Edw. 



areolated, Fig. 52, C). The last four genera contain many common 

 British 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. HOLOSOMATA. 



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. 53). Ascidiozooids having 

 the intestine and reproductive organs by the side of the branchial 

 sac (Fig. 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 Botryllus, Gaertn. 

 and PalL, with simple stellate systems (Fig. 53), and Botrylloides, 

 Milne-Edwards, with elongated or ramified systems. There are 



