36 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



Cephalodiscus and Rhabdopleura, two sessile forms formerly classed 

 as Order, Pterobranchia, under Bryozoa, have been found to resemble 

 Balanoglossus. In young buds of the former a division into proboscis, 

 collar, and body may be seen. There is also a single pair of gill-slits, and 

 a dorsal diverticulum of the intestine (= notochord ?) lying under the 

 dorsal nervous system. In Rhabdopleura no gill-slits have been detected, 

 but in other respects the structure is similar to Cephalodiscus. 



Class II. TUIflCATA A group of marine animals which 



are free-swimming during larval 

 life at least, and which possess an 

 endoskeletal rod (notochord) in 

 the tail. The body of the adult 

 is enclosed in a mantle or ' ' tunic, ' ' 

 which may be gelatinous, leathery 

 or cartilaginous, and possesses an 

 incurrent or oral and an excurrent 

 or anal orifice. The pharynx is 

 perforated by gill-slits which may 

 become so numerous as to convert 

 the entire pharyngeal wall into a 

 lattice-work. Many species are 

 sessile when adult and in these the 

 intestine becomes U-shaped and 

 the two mantle openings approxi- 

 mate one another, while in the 

 free-swimming forms the intestine 

 is straight and the two orifices are 

 situated at the ends. 



Sub-class I. PEREinncHORSATA. . . .Free-swimming forms, resembling 



the larvae of higher Tunicates. 

 They possess a long tail provided 

 with a skeletal axis, the notochord. 

 Pharynx with a single pair of gill- 

 slits. No definite mantle but a 

 gelatinous envelope. 



X Appendicularia. 



Sub-class II. ASCIDIACEA Body sac-like, with pharyngeal 



wall completely perforated with 



