132 



THE VOYAGE OF H.M.S. CHALLENGER. 



Fig. 21.— Diagram of part of a Compound Asoidian colony belonging to the PolycliniJa 

 showing two Ascidiozooids united to form a system. 



and 



fi. anus ; at. atrial .aperture opening into the common cloacal cavity ; Br. branchial aperture ; br.s. branchial sac ; 

 rl. common cloacal aperture; cc. ectoderm; en. endostyle ; gl.n. subneural gland; h. heart; i. intestine; 

 i.gl. intestinal gland ; /. languet ; m. mantle ; n.g. nerve ganglion ; a:, cesophagus ; or. ovary ; p.p. peripharyngeal 

 band; r. rectum; st. stomach; t. test; tn. tentacle; t.r. testis; v. up. vascular appendage; f.il. v.as deferens. 

 The limits of the thQra.\, abdomen, and post-abdomen are shown by the dotted lines on the left hand side. 



