TOO 



THE VOYAGE OF H.M.S. CHALLENGER. 



gramma, 0. F. Miiller, and suggested that it should be separated from the other species 

 of Ascidia as a new genus ; but this was not formally done until Hancock, in 1870, pub- 

 lished a paper in the Annals and Magazine of Natural History, containing descriptions of 

 a laro-e number of new species of British Tunicata, two of which, Corella larvceformis 

 and Corella ovata, he referred to the newly-made genus. He defined the genus chiefly 

 by the peculiarities which Alder had pointed out seven years before as distinguishing 

 Corella parallelogramma, namely, the position and course of the alimentary canal, the 

 position of the heart upon the right side of the branchial sac, and the spiral interstig- 

 matic vessels. 



The Challenger expedition added a third species (Corella japonica), from the Japanese 

 Seas, and quite recently (1881), Traustedt has described two new species (Corella minuta 

 and Corella eumyota) from the West Indies. 



These different species may be distinguished according to the following table : — 



Corella. 



Atrial aperture anterior. 



Atrial aperture dorsal. 



Placed upon a very 

 long projection. 



I 

 0. larvceformis. 



Sessile. 



Musculature strong 

 on left side. 



I 

 C. parallelogramma. 



Musculature very weak 

 on both sides. 



I 



C. minuta. 



Anterior end of body wide. 



Atrial aperture not far from 



branchial. 



I 

 C. ovata. 



Anterior end of body narrow. 



Atrial aperture distant from 



branchial. 



Tentacles of two 

 sizes. 



I 

 C. eumyota. 



Tentacles all of 

 one size. 



I 

 C. japonica. 



Corella japonica, Herdman (PI. XXVI.). 



Corella japonica, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1879-80., p. 472. 



External Appearance. — The shape is ovate or longish ovate, the anterior end being 

 narrower than the posterior, which is rounded ; the ventral edge is rather more convex 

 than the dorsal. The body is somewhat compressed laterally, and is attached by the 

 posterior end and the posterior half of the lower or right side. The base is occasionally 

 produced into short tufts for attachment. The branchial aperture is terminal or sub- 

 terminal, being slightly on the left side of the anterior extremity. The atrial is about 



