III ASCIDIAE COMPOSITAE—DISTOMATIDAE 85 
Group 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 
of Colella peduncu- 
2 lata, Q. and G., nat. 
71600 a Bona oe 
end-)) MDI) 
(HNN 
Er Fie. 47.—A, Colony 
zone of reproduc- 
ing adults; d, old 
decaying adults and 
incubatory pouches 
with larvae. ~B, 
Ascidiozooid, with 
incubatory pouch 
enlarged : Af, atrial 
aperture ; Br, bran- 
chial aperture ; em, 
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, Della Valle, and Colel/a, 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 ' 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. 
