12 MORPHOLOGY OP 



Another feature which ought not to be overlooked in a 

 general account of this species (B . K o w a 1 e v s k i i) is its extreme 

 vitality. In a bucket of unaerated water in which all other animals 

 had died some days beforCj in a hot climate, these creatures were 

 able to carry on their existence, and parts of the body may be seen 

 moving about by means of the ciliated skin to which a com- 

 pletely macerated skeleton of the branchiae is attached. Lobes 

 of the testis, torn off, will likewise swim about for days. To 

 what extent the body is capable of regeneration I cannot say. 

 Specimens were found in which there was at all events an 

 appearance suggesting that the proboscis had grown again, 

 Spengel has alluded to regeneration of tissues as occurring in 

 B. minutus, and I have little doubt that it is also common in 

 B. Kowalevskii. 



With regard to the specific name of this form, it appears 

 that the figure and description given by Agassiz of B. Kowa- 

 levskii identify it with the form which is the subject of this 

 paper. The mode of development ascribed by him to the 

 species is of course entirely different. Seeing, however, that 

 he was unable to show the connection between the animals 

 found by him in the beach and the Tornaria which he reared, 

 it does not seem by any means certain that these Tornaria 

 were the larvse of B. Kowalevskii. On the whole, it is 

 at least possible that they were the young of some other 

 species, e.g. B. Bro.oksii, which occurj at least as far 

 north as the Chesapeake, and probably higher still on the 

 coast. 



From a general survey of the group Enteropneusta, which I 

 hope subsequently to attempt, I think it will appear likely that 

 B. Kowalevskii stands, in many respects, in a group differing 

 in several features from the other members, which agree with 

 one another in these points, e. g. short proboscis, complicated 

 branchial skeleton, operculum small, liver saccules present, eggs 

 minute, &c. It is to the latter division I am inclined to 

 believe that Tornaria alone belongs. 



In studying the anatomy of Balanoglossus by means of 

 sections difficulty arises owing to the variable amount of con- 



