DESCRIPTION OF THE SPECIES. 



ASCIDLE SIMPLICES. 



The Ascidise Simpliees, in which I include the Clavelinidse, may be denned as solitary 

 or social, fixed or free, but never free-swimming, Ascidians, which may reproduce by 

 gemmation so as to form societies of Ascidiozooids united by a common vascular system, 

 but in which each has a distinct test, and is not imbedded along with the other Ascidio- 

 zooids in a common investing mass. 



This suborder, then, includes those Ascidians which are never free-swimming and arc 

 never imbedded in a common colonial mass. They are usually solitary, and reproduce 

 only in a sexual manner. In at least one family, however, reproduction takes place also 

 by gemmation, which results in the formation of small colonies or " societies," but in 

 these the different ascidiozooids are perfectly distinct, and their tests are not united into 

 a common investing mass, as in the Ascidise Composite. They are merely joined by 

 their posterior ends, usually by the intervention of a creeping stolon containing blood- 

 vessels, so that the different members are connected by a colonial circulatory system. 



This family, the Clavelinidse, has usually been considered as a distinct suborder 

 (Ascidise Sociales), of equal rank with, and intermediate between, the Ascidise Simpliees 

 and the Ascidia? Composite ; while it has sometimes been united with the last-named 

 group to form the suborder Synascidiae. I have already, in the Preliminary Report, 1 given 

 in detail my reasons for placing the Clavelinidse in the Ascidise Simpliees. 



The Ascidise Simpliees may be divided into four families — the Molgulidse, the 

 Cynthiidaa, the Ascidiidaa, and the Clavelinidse. In the last of these, gemmation and 

 the formation of a colony take place ; while in the others, although the apparatus for 

 budding — the " blood-vessels " of the test — is present, and may even be developed into 

 stolon-like processes, so far as is known buds are never formed. In this property, the 

 power of reproducing by gemmation, the Clavelinidse differ from the other Ascidiaa 

 Simpliees ; otherwise they closely resemble the Ascidiidse, such genera as Ecteinascidia, 

 Ciona and Rhopalcea forming a passage from the one family to the other. 



The Cynthiidse and the Molgulidae are more nearly allied to each other than to the 

 Ascidiidse, which family is less highly developed and less complex in organisation than 

 the two former. The Molgulidse are probably the most highly differentiated and most 

 elaborately complete in all their parts, while the Clavelinidas may be considered as the 



1 Proc Roy. Soc Ediii., 1879-80, p. 714. 



