266 



SYSTEMATIC ZOOLOGY 



FlG. 277. Botryllus violaceus. Two 

 colonies, cl, common cloacal or atrial 

 opening; or, oral or branchial openings. 

 (After Milne-Edwards, from Parker and 

 Haswell's Manual.) 



peculiar power of sending the 

 blood alternately in opposite direc- 

 tions. The nervous system is a 

 single dorsal ganglion with nerve 

 fibers going to various parts of the 

 body (Fig. 275). The Tunicata 

 are hermaphroditic ; the ovary and 

 testes lie near each other, and 

 their ducts open on the dorsal side 

 of the body into the atrium near 

 the anus. Cross fertilization gen- 

 erally takes place, however, since 

 the ova and spermatozoa do not 

 mature simultaneously in the same 

 individual. 



The structure of the free-swim- 

 ming Tunicata (Fig. 276) is essen- 

 tially like that of the ascidian just 

 described, but the tunic is very 

 thin, and the branchial and the atrial apertures are at opposite 

 ends of the body, which 

 is usually more or less 

 barrel-shaped, with the 

 muscle bands of the 

 mantle arranged circu- 

 larly like hoops. In the 

 compound Tunicata the 

 individuals are all in- 

 closed in a common con- 

 tinuous tunic ; there is 

 a branchial aperture for 

 each individual, while 

 sometimes there is a 

 single atrial aperture for 

 the whole colony, as in 

 Botryllus (Fig. 277), and 

 sometimes each individ- 

 ual has an atrial pore F iCi - 2 ?%' jP,, '' , ' f, ""' ! ' a colonial tunicate. A, lateral 

 . aspect; B, end view. (After Herdman, from Parker 



Which opens llltO a large and Haswell's Text-book.) 



B 





