Dr. L. Plate on Asellicola digitata. 215 



retracts all the tentacles and moves away in a fashion which 

 I shall fully describe further on. In individuals engaged in 

 conjugation we usually find the tentacles unaltered ; some- 

 times, however, they are only developed laterally upon the 

 right or the left half of the body, but generally without any 

 agreement in this respect between the two united animalcules. 

 Lastly, it may be remarked that the sucking-tubes at their 

 first appearance in the form of pale, narrowly conical processes 

 of the body do not possess any tentaculets ; but as soon as 

 they have attained about one third or one half of their defi- 

 nitive size this retractile terminal member also makes its 

 appearance. 



With regard to the reproduction of Asellicola I may be 

 brief, because it exactly resembles that of Dendrocometes 

 paradoxus, which I have already described in detail. Here, 

 indeed, the bud-formation is by no means so easy to observe 

 as in the above ectoparasite of Gammarus pulex, because the 

 plasma of Asellicola is far more densely granular and less 

 transparent. The formation of the swarm-buds is first indi- 

 cated by the appearance of a second contractile vacuole below 

 the middle of the dorsal surface. There is formed, from the 

 back, a flask-shaped invagination, which finally, by the 

 closing of the external opening, produces a cavity closed all 

 round and situated in the interior of the cell. The next stage 

 leaves the observer no room for further doubt that we have 

 here really to do with reproduction. We observe, nearly 

 parallel to the basal surface and surrounding the inner cavity 

 equatorially, a circlet of long cilia (fig. 5), which strike 

 irregularly to and fro. After this first band of cilia two others 

 are formed, and at the same time the bottom of the cavity is 

 driven up into a hump, so that it closely approaches the roof, 

 leaving only a narrow fissure between them. Lastly, a fresh 

 aperture is produced upon the back, leading into the brood- 

 cavity ; the bud, z. e. the part driven up, pushes itself through 

 this aperture, and only then becomes constricted off from the 

 parent-animal. The division of the nucleus also takes place 

 only at the moment of the liberation of the bud by simple 

 constriction of the maternal nucleus, which has been some- 

 what elongated. The spot where the young animal separates 

 from its parent is not a fixed point upon the back, but is 

 situated sometimes in one place sometimes in another. 



Ihe freely motile young stage of Asellicola digitata has 

 nearly the same form as the adult animal, only the dorsal 

 surface is less convex and the body of course much smaller 

 (0-048 millim. in length and 0"02 millira. broad). The plane 

 lower surl'ace bears three oval circlets of cilia (fig. 6), which 



