ASCIDIAE COMPOSITAE DISTOMATIDAE 



GBOUP A. MEROSOMATA. 



Viscera posterior to branchial sac ; budding stolonial. 



Fam. 1. Distomatidae. Ascidiozooids divided into two 

 regions, a thorax, containing the branchial sac, and an abdomen, 

 with the remaining viscera (Fig. 47, B); testes numerous; vas 

 deferens not spirally coiled. The chief genera are Distoma, 

 Gaertner, with some British species ; Chondrostachys, Macdonald, 

 Cystodytes, v. Drasche, with calcareous plate-like spicules in the test 



rf., 



mcp. 



3 



FIG. 47. A, Colony 

 of Colella peduncu- 

 lata, Q. and G., nat. 

 size: a, zone of buds; 

 b, zone of young 

 ascidiozooids ; c, 

 zone of reproduc- 

 ing adults ; d, old 

 decaying adults and 

 incubatory pouches 

 with larvae. B, 

 Ascidiozooid, with 

 incubatory pouch 

 enlarged : At, atrial 

 aperture ; Br. bran- 

 chial aperture ; emb, 

 embryos ; end, en- 

 dostyle ; ep.c, epi- 

 cardium ; inc.p, 

 incubatory pouch ; 

 od, oviduct ; od', 

 its prolongation 

 into inc.p ; od", its 

 termination at tip 

 of inc.p ; ov, ovary ; 

 p.br, peribranchial opening of inc.p ; st, stomach. 



(Fig. 50, A); Distaplia, Delia Valle, and Colella, Herdman, forming 

 a pedunculated colony (Fig. 47, A), in which the ascidiozooids (Fig. 

 47, B) are provided with large incubatory pouches, opening from 

 the peribranchial cavity, but also connected, as Bancroft l has re- 

 cently shown, with the end of the oviduct (see Fig. 47, B). In 

 these pouches the embryos undergo their development, and are 

 set free by the decay of the top of the colony. The stolons pass 

 from the ascidiozooids in the upper part of the colony down into 

 the stalk, and there produce buds which gradually work up to 

 the top of the stalk, where they take their places as young ascidio- 

 zooids. At the top of the colony the old ascidiozooids die 

 and are removed (see Fig. 47, A). Caullery has shown that in 



1 Bull. Mus. Comp. Zool. xxxv. No. 4, 1899, p. 59. 



