Dr. A. Krohn on the genus Doliolum and its species. 135 



Sexual individuals were not seen. In the asexual ones the 

 ante-penultimate muscular band has the same arrangement as in 

 D. Nordmanni*. 



Development and Metamorphosis. 



The development of the buds was observed in D. Mulleri, but 

 presented no remarkable feature. The buds shoot one after 

 another, as it seems, from the gemmarium, for the outermost is 

 always the largest, and often already changed into a young 

 Ascidian, whilst the others are far behind in their development, 

 and indeed the more, the greater their distance from it. Buds 

 which are so far developed as to allow the majority of the organs, 

 and among the rest the swiftly pulsating heart, to be distin- 

 guished, are placed vertically (like those of the Compound Asci- 

 dians and Clavelinidse according to Milne-Edwards), with the 

 anterior extremity forwards, and are attached to the gemmarium 

 by a short pedicle. This pedicle is inserted upon the abdominal 

 surface close below the alimentary canal ; when the bud is de- 

 tached it falls with it, and subsequently wholly disappears. Such 

 recently detached budded forms may be so far confounded with 

 young asexual individuals, inasmuch as their pedicle may be 

 readily taken for the little-developed and as yet budless gemma- 

 rium, which has the same form and position. More close exa- 

 mination, however, will eliminate this error, since all free bud- 

 forms already exhibit the rudiments of the sexual organs. 



The asexual individuals developed from ova are born, as has 

 been said, in the form of Cercaria-like larvae, and therefore un- 

 dergo a metamorphosis. This metamorphosis is characterized, 

 howevei', by many peculiarities, whose explanation is only to be 

 found in the mode of life of the adult animal. It is well known 

 that in the larvae of the fixed Ascidians, the tail very soon disap- 

 pears, as an organ which has become useless, when the larva has 

 found a fitting locality in which to fix itself. Only after this has 

 taken place does its body become gradually changed into the 

 perfect animal. 



In Doliolum, on the other hand, which, as we have seen, is a 

 free swimmer, there is no need for the tail to disappear so soon ; 



* I must leave it undecided whether the cask-like Tunicary with eight 

 muscular bands, but much larger than D. denticulatum, which is described 

 by Quoy and Gaimard as D. caudatum {I. c. p. 601, pi. 89. fig. 29. & 30), really 

 belongs to this genus. In the figure the one end of the body is indeed 

 siphon-like, but its lip is without lobes. From the opposite extremity a 

 dense pyramidal process projects, like the processes of many associated 

 SalpcE. I should be inclined to regard the animal rather as a Salpa than as 

 a Doliolum, especially since the completely circular muscular bands which 

 it possesses, are, as we have seen above, no decisive criterion of the genus 

 Doliolum. 



