44 



members are not buried in a common investing mass, 

 but each has a distinct test of its own. No strict line of 

 demarcation can be drawn between the Simple and Com- 

 pomid Ascidians, and one of the families of the former 

 group, the Clavelinidse (the Social Ascidians), forms a 

 transition from the typical Simple forms, which never 

 reproduce bj' gemmation to the Compound forms, which 

 always do. 



The Ascidise Simplices may be divided into the follow- 

 ing families : — 



Family I. Clavelinid^ : — Simple Ascidians which 

 reproduce by gemmation to form small colonies, in which 

 each Ascidiozooid has a distinct test, but all are connected 

 by a common blood-system. Buds formed on stolons, 

 which are vascular out-growths from the posterior end of 

 the body containing prolongations from the ectoderm, 

 mesoderm, and endoderm of the Ascidiozooid. Branchial 

 sac not folded ; internal longitudinal bars usually absent ; 

 stigmata straight ; tentacles simple. 



This family contains three chief genera — Ecteinascidia, 

 with internal longitudinal bars in branchial sac ; Glavelina, 

 with intestine extending behind branchial sac ; and Pero- 

 phora, with intestine alongside branchial sac. Glavelina 

 lepadiformis and Perophora listeri are common British 

 species found at a few fathoms depth off various parts 

 of our coast. Both occur round the south end of the Isle 

 of Man, 



Family II. Ascidiid^e : — Solitary fixed Ascidians with 

 gelatinous test ; branchial aperture usually 8-lobed, atrial 

 aperture usually 6-lobed. Branchial sac not folded ; in- 

 ternal longitudinal bars usually present ; stigmata straight 

 or curved ; tentacles simple. 



This family contains, along with several other genera, 



