46 



Sub-order II. AsciDi^ Cuaipositji:. 



Fixed Ascidians which reproduce by gemmation, so as 

 to form colonies, in which the Ascidiozooids are buried in 

 a common investing mass, and have no separate tests. 

 This is probabl}' a somewhat artificial assemblage, formed 

 of two or three groups of Ascidians which produce colonies 

 in which the Ascidiozooids are so intimately united that 

 they possess a common test or investing mass. This is 

 the only character which distinguishes them from the 

 Clavelinidfe., but the property of reproducing by gemma- 

 tion separates them from the rest of the Ascidia3 Simplices. 

 The Ascidiae Compositae may be divided into the following 

 families : — 



Family I. Distomid^ : — Ascidiozooids divided into two 

 regions, thorax and abdomen; testes numerous ; vas deferens 

 not spirally coiled. The chief genera are — Distoma, Dis- 

 taplia, Colella, the last forming a pedunculated colony, 

 in which the Ascidiozooids develop incubatory pouches, 

 opening from the peribranchial cavity, in which the 

 embryos undergo their development. 



Family II. Ccelocormid^ : — Colony not fixed, having 

 a large axial cavity with a terminal aperture. Branchial 

 apertures 5-lobed. This includes one species, Ca'locornms 

 huxleyi, which is a transition form between the ordinary 

 Compound Ascidians (e.g., DistomidseJ and the Ascidioe 

 Luciae (Pyrosoma). 



Family III. Didemnid^ : — Colony usually thin and 

 incrusting. Test containing stellate calcareous spicules. 

 Testis single, large ; vas deferens spirally coiled. The 

 chief genera are — Didemnum, in which the colony is thick 

 and fleshy, and there are only three rows of stigmata on 

 each side of the branchial sac ; and Leptoclimnn, in which 

 the colony is thin and incrusting, and there are four rows 



