218 Dr. L. Plate on Asellicola digitata. 



described, to about half the height of the individuals, it swells 

 up still more iu the middle (fig. 10), so that frequently, in 

 each pair, the adherent disk, originally situated in the centre 

 of the underside, comes, by the displacement of the plasma, 

 to be situated at one end of the body ; and then follows the 

 stage which I have briefly indicated above, and which attracts 

 our interest in the highest degree — the nuclei of both indi- 

 viduals of a pair, which hitherto have shown no alteration (or 

 at the utmost sometimes an extension in length), migrate into 

 the canal of union and towards one another, at the same time 

 bend the approximated ends dov/nwards at a right angle 

 (about one third of the whole length), and in this form closely 

 approach each other (fig. 10). I have never met with indi- 

 viduals of which the nuclei were directly in contact ; but 

 there was always a narrow wall of plasma between them, and 

 this was sometimes so wide that the above-mentioned mem- 

 branous lamella could be developed in it. It would of course 

 be going too far if we were to deny the possibility of a tran- 

 sitory actual fusion of the nuclei, for it is quite conceivable 

 that this stage of the conjugation may have escaped my 

 notice. On the other hand, however, there are at present no 

 grounds for assuming anything of the kind, because there is 

 no doubt that during this period of mutual approximation the 

 nuclei undergo no change of structure. 



After the nuclei have thus reciprocally influenced each 

 other for a time (how long I am unable to say) they migrate 

 back into their original position, at the same time assuming 

 their old form. Simultaneously with this the plasma returns 

 out of the canal of union into the proper cell-body, and the 

 former in consequence becomes narrower and narrower 

 (fig. 8), until it finally ruptures in the middle and its remains 

 are completely retracted by the respective individuals. Even 

 at the time represented in fig. 8 (see the animal to the left), 

 or only when the paired individuals have separated from each 

 other, the nuclei begin to divide and to become constricted, 

 and they finally break up into a number of larger and smaller 

 pieces, which are scattered through the whole of the cell- 

 body. Unfortunately I have not succeeded in ascertaining 

 unmistakably the regeneration of the new nucleus. As the 

 AselUcolce cannot be kept long alive in the damp chamber I 

 was compelled to deduce the course of the conjugation from 

 the combination of as many individual stages as possible, 

 which, from the simplicity of the whole process, can hardly 

 aftect injuriously the accuracy of our judgment. The final 

 stage, unfortunately, has only once come under ray observa- 

 tion, and according to this the new nucleus in each paired 



