INTRODUCTORY OBSERVATIONS. 5 



and endocyst ; but, inasmuch as their constitution is in all probability fundamentally the 

 same throughout, that is to say, in the permanently membranous portion, as in the rigid 

 part or true cell, the former terms would seem to be rather more appropriate. Be 



t.t. Tentacles. 



I. Lopliophore. 



m. Mouth. 



g. Nervous ganglion. 



a. Anus. 



. (Esophagus. 



v. Tentacular sheath, or vaginal por- 

 tion of integument. 



t. Intestine. 



or. Orifice of calcareous cell. 



c. Calcareous or rigid portion of 

 integument. 



o. Ovary. 



x. Testis. 



s. Stomach. 



p.p. Protrusor muscles. 



r.r. Retractor muscles. 



this as it may, the solidifying material, whatever its nature, belongs to the external tunic, 

 which is in all respects comparable to the external coat or test of an Ascidian, whilst the 

 internal tunic is soft, transparent, and contractile. In consequence of the marked 

 difference just indicated between the upper and lower portions of the integument, the 

 latter in most cases forms a sort of cup or receptacle into which the upper or flexible 

 portion, together with the parts attached to it, can be drawn by appropriate muscles. Now 

 the parts attached, or in immediate connexion with this flexible portion, are 1, the 



