On the Synascidia of the Oenus Colella. 133 



places, one transverse and the other somewhat oblique. 



4 e. One of the bristles of the embryo, highly magnified. 

 Fig. 5. Hormurus cmstralasice. 



oa. Ventral view of anterior part of embryo. The chelicerEe are 



concealed by the large chelae. X y. 



5 b. Transverse section through distal part of chelte and the secre- 



ting cells (sc) surrounding them, sc', dorsal secreting cells. 



125 

 X 1- 



Fit/. 6. Palamncsus Thorellii. Dorsal view of embryo X y. 



XVIII. — On the Synascidia of the Genus Colella and the 

 Polymorphism of their Buds. By M. MAURICE CauLLERY *. 



The genus Colella, created by Herdmann for the Synascidia 

 collected by the ' Challenger' expedition, belongs to the family 

 of the Distomidaj, and is very nearly related to Distaplia. 



Among the compound Ascidians in the Museum, the study 

 of which has been entrusted to me by M. Edm. Perrier, there 

 are a certain number of representatives of this genus, some of 

 them from Australia (' Astrolabe ' expedition), others from 

 Cape Horn. Thanks to this material, I have been able to 

 obtain a certain number of facts connected with the anatomy, 

 relationships, and blastogenesis of these animals, which I 

 shall set out later in detail. Here I shall only point out the 

 following : — 



(1) The species whicli I have had under examination 

 present all four rows of pores. A specially characteristic 

 arrangement is to be noticed : the second and the third row 

 separate one from the other in the portion near to the endo- 

 style in such a manner as to leave between them a triangular 

 space, not perforated by pores. The pores are not divided 

 into two halves by a transverse band, as in the Distaplia. 

 These two characters appear to me to be very suitable as a 

 definition of the genus Colella. 



(2) The examples of Corms which I have examined are 

 unisexual, a fact already determined by Herdmann for several 

 species ; further, in a female Corm the buds only present 

 ovules, in a male Corm only spermatic vesicles; so that, 

 so far as the material at my disposal would allow me to do so, 

 1 conclude that there is for each Corm a defined sexuality, 



* From the ' Coruptes Rendus,' tome cxxii. 1896, pp. 1000-1069. 



