CLASSIFICATION OF THE TIJNICATA. 605 



Suborder II. A8CIBIM COMPOSITjE, Saviguy, 1816. 



This group contains fixed Ascidians which reproduce by gem- 

 mation so as to form colonies in which, the ascidiozooids are 

 buried in a common investing mass, and have no separate tests. 



The Ascidia) Compositse include seven families. It should be 

 remembered that they are in all probability a polyphyletic group, 

 having been derived from several distinct groups of ancestral 

 Simple Ascidians. They are thus a semi-artificial assemblage 

 consisting of those fixed Ascidians which have retained or 

 acquired the power of reproducing by gemmation, so as to form 

 colonies, and in which the ascidiozooids have remained so inti- 

 mately united that their tests form a common colonial mass. 



Family I. BOTEYLLID^, Giard, 1872. 



Colony usually thin and iucrusting, sometimes in the form of 

 thick fleshy masses. 



' Systems circular, elliptical, or forming branched lines. Common 

 cloacal openings distinct, usually lobed. 



Ascidiozooids short and not divided into regions. 



Test usually soft, traversed by numerous vessels with large 

 terminal knobs. 



Branchial sac large and well developed, internal longitudinal 

 bars present, stigmata numerous. 



Dorsal lamina in the form of a plain membrane. 



Tentacles simple, not more than 16 in number. 



Alimentary canal placed alongside the posterior part of the 

 branchial sac. 



Gonads on both sides of the body. 



Gemmation lateral, from the bodies of the ascidiozooids ; and 

 also stolonial, from the ectodermal processes or vessels in the test. 



This family includes five genera, which may be distinguished 

 as follows : — 



j Colony stalked. Gonads unpaired, in intestinal loop. Symplegma. 



I Colony sessile. Gonads paired, placed laterally 1 



^ J Systems circular in outline 2 



\ Systems elongated or branched irregularly 3 



nf Colony thin, iucrusting Botryllus. 



[Colony thick and fleshy Polycyclus. 



„ r Colony thin, incrusting Botrylloides. 



I Colony tliick and fleshy Sarcobotrylloides. 



