Dr. A. Krohn on the genus Doliolum and its species. 123 



eventually upwards upon the right side of the cavity of the 

 body. 



In the sexual individuals of this species I have only been able 

 to discover the males, and I thence presume that the sexes are 

 separate. The male apparatus lies upon the left lateral wall of 

 the posterior cavity, and consists of a testis and a relatively long 

 and wide seminal canal. This canal is commonly distended with 

 spermatozoa, and extends as far as the fourth muscular band. 

 The testis is composed of single rounded lobes, which, like the 

 folioles of a rosette, are grouped round the commencement of 

 the seminal canal. 



As to the asexual individuals, the change in the arrangement 

 of their muscular bands produced by the development of the 

 gemmarium, consists in the separation of the ends of the penul- 

 timate band ; the narrow and pointed extremities of which run 

 for some distance upon the base of the gemmarium. Fully de- 

 veloped individuals of this kind attain the length of 2 lines or a 

 little more. 



2. Doliolum Millleri (Krohn). 



This species is wider in the middle, and thence resembles a 

 more squat cask. The mantle is very soft and almost mucila- 

 ginous, so that foreign bodies readily become imbedded in it. 

 The branchial membrane has the form of a vertical partition 

 placed in the posterior part of the cavity of the body and slightly 

 convex behind ; there are about twelve pair of clefts. The mouth 

 seemed to be nearer the lower half. The alimentary canal, on 

 the other hand, is in the middle of the cavity, remote from either 

 wall. The oesophagus descends towards the stomach, to which 

 the short intestine succeeds, descending at first and then curving 

 upwards in a loop. 



The sexual individuals of this species are hermaphrodite. Close 

 to the stomach and intestine we distinguish three structures 

 closely applied to one another. The largest, the testis, is pyri- 

 form, and lies with its narrower end near the anus. The two 

 other bodies are spherical ; the one is filled with clear nucleated 

 vesicles, which I consider to be germs ; whence the whole must 

 be regarded as an ovarium. The other body is unquestionably 

 a fully developed ovum, in which we easily recognize the outer 

 investment, the granular yelk and the germinal vesicle with its 

 spot. In some individuals I found it free, in the posterior cavity 

 of the body. 



With regard to the asexual individuals I will only observe, that 

 their penultimate muscular band is arranged similarly to that of 

 the preceding species. 



Varieties of this very common species, which is often met with 



