l>si; 



THE VOYAGE OF H.M.S. CHALLENGER. 



must have been a form with no peduncle, simple tentacles, internal longitudinal bars and 

 folds in the branchial sac, with the stomach probably posterior, and having no power of 

 gemmation. Such a form is represented, probably with little change, by the genera 

 Stt/ela aud Polycarpa, while Bathyoncus has diverged at the point 7. Pelonaia, which 

 like Bathyoncus differs from the other Styelime in having the branchial sac modified, is 

 probably of comparatively -recent formation, as some of the species of Styela show 

 tendencies in the same direction, — i.e., towards the loss of the branchial folds. From the 

 main stem between C. and Styela, a form D. has branched off, which had compound ten- 

 tacles, and was the common ancestor of the Cynthinas, the Bolteninse, and the Molgulidse. 



Phylogenetic Table of the Ascidi^e Simplices, 



Ascopcra. 

 Molgula. 



Clenicella, 



Culcolua. 

 Fimgulus. 



Eugyra. 



No folds in 

 branchial sao, 



10. 



Boltcnia. 



Branchial sac modified. 



Cynthia. 

 9. Microcosmus. 



Peduncle. 



E. Stigmata 



curved and 



generally in 



spirals. 



Styela. 

 Polycarpa. 



Bathyoncus. 



D. Tentacles compound. 



Branchial sac modified. 

 I 7. 



Fachychl&na. Abyssascidia. 

 Aseidia. Corella. 



Ciona. 



Stomach on 

 left side. 



C. Branchial sac folded. 6. 

 I 



Stomach on 

 right side. 



No reproduction 



by gemmation. Ecicinascidia. 



4. 



PerqpAora. 



Clavel.ina. 



Peduncle. Stomach on 

 | 3. Peduncle, left side. 



B. Internal longitudinal bars 

 iu the branchial sac. 



A. Body not pedunculated : 



branchial sac not folded, and 



with no internal longitudinal bars ; 



stomach posterior to branchial sac ; 



tentacles simple. 



A, B, C, D, aud E are hypothetical ancestral forms of large groups, while 1-10 are points where a change of strncture 

 is supposed to have taken place, resulting in the divergence of one or more genera from the main line. 



