36o TUNIC ATA. 



DIAGRAM XIX. 



TUNICATA. 



Figs. A, B, and C (after Ray Lankester) illustrate how a larval 

 Ascidian degenerates into the adult form. 



Ta , tail; Not, notochord ; Br., brain; M., mouth; Gi.-sl., gill- 

 slits ; CI. , cloacal chamber. 



The figure of a simple Ascidian represents an animal opened on the 

 right side, but the gut and reproductive organ {rep.) on the left are sup- 

 posed to be shining through. The mouth {m.), the latticed pharynx, 

 with dorsal ridge and ventral groove {v. g.), the coiled gut, the cloaca 

 {cl.), the dorsal ganglion {gn.), the ventral heart {h.') are indicated. 

 Around the body is the tunic. 



The section to the right shows the external tunic, beneath which is 

 the body-wall, within which, surrounding the pharynx {ph.), and open- 

 ing into the cloacal chamber, is the peribranchial cavity (/. b. c). 



Beneath, some stages in the development are shown (after Hseckel). 

 A, the ovum ; B, the first four cells ; C, a section of the gastrula ; D, 

 a young embryo, showing gut (ff), neural canal («. c), and notochord 

 (w-'.). 



