122 Dr. A. Krohn on the genus Doliolum and Us species. 



But while in the former this double means of multiplication is 

 allowed to each single creature, in the latter each generation 

 possesses only a single mode ; so that, as in the Salpa, the first 

 generation propagates by ova, and the second multiplies by bud- 

 ding, the third again producing ova, and so on in a continual 

 alternation. In support of this view I may adduce the fact, that 

 on examining a certain number of adult individuals of the same 

 kind, in some, generative organs are always found, in others only 

 a stolo prolifer — the producer and bearer of the gemmae. Further 

 evidence will be adduced in the section upon Development. 



In the sexual generation the male and female organs are 

 sometimes united in the same, sometimes carried by different 

 individuals. The gemmarium {keim-stock) of the asexual indi- 

 viduals is a short, cylindrical, somewhat curved, posterior pro- 

 cess, which arises close in front of the posterior aperture and 

 exactly in the middle line ; in some species upon the dorsal, in 

 others upon the ventral side. It can be moved to a slight extent, 

 by one of the posterior muscular bands, which appears to be 

 peculiarly modified for this purpose in all asexual individuals ; 

 of which more by and by. The buds, whose number is but 

 small, are developed only from the extremity of the gemmarium, 

 along which we find them arranged one behind the other as 

 more or less projecting prominences. 



The asexual generation, developed from ova, has to undergo a 

 metamorphosis. As in other Ascidians the larva is Cercariform. 



All the species move by jerks, as Quoy and Gaimard state ; by 

 a sudden contraction they dart forwards, and then remain at rest 

 for awhile. 



Description of Species. 



A. Species with eight muscular bands and the gemmarium 

 ventral. 



1. Doliolum denticulatum^ (Q. & G,). 



The branchial membrane is bent into a sharp angle projecting 

 backwards, and extends further than in the succeeding species. 

 Its upper half reaches as far as the second muscular band, and 

 at times beyond it ; the lower half extends as far as the third 

 muscular band only. 



The mouth is placed upon the lower half of the branchial 

 membrane ; from it the CEsophagus passes in a curved direction 

 backwards and downwards to the deeper-seated stomach. The 

 intestine descxibes a wide arc, passing at first backwards and 



* This specific denomination is unfitting, since in the other species the 

 anterior aperture is toothed. I propose therefore for this species the name 

 of D. Ehrenbergii. 



