Dr. L. Plate on Asellicola digitata. 217 



tata consists in its conjugation. Although in many points of 

 its progress this agrees with the same process in Dendroco- 

 metes, there is an essential difference between the two, which 

 is much in favour of the view that the conjugation of the 

 Infusoria represents a sort of foreshadowing of the act of 

 fecundation. Thus it comes to a stage in which the nuclei of 

 both animals lie close together for a considerable time and 

 then separate from each other, a process which seems to indi- 

 cate a reciprocal influence of the nuclei. As the Asellicol(2 

 in general do not sit so close together that they touch each 

 other, and therefore can directly become fused together, those 

 individuals which are about to conjugate are almost always 

 compelled to unite themselves by means of a process of the 

 body. For this purpose they avail themselves of one of the 

 tentacles situated at one end of the body, which then grows 

 enormously beyond its ordinary size. Fig. 7 shows a Sue- 

 torian in this stage, and exhibits very plainly the structure of 

 the tentacle, and especially the presence in it of a central 

 longitudinal canal. Frequently I found two animals seated 

 near each other, both of which displayed a " conjugation- 

 tentacle " of this kind, so that here both had evidently endea- 

 voured to conjugate, while in other cases only one of the 

 pair furnished the bridge of union. The conjugation-tentacle 

 is slowly moved to and fro by the Asellicolce, as if feeling 

 about, until they have attained their object. The animals 

 are apparently in a high degree governed by the desire for 

 such a union, for one must often wonder at the size of the 

 canals which are produced for this purpose ; they are fre- 

 quently longer than the individual animals. When the two 

 individuals have succeeded in uniting, the fissure in the 

 plasma originally destined to conduct nutriment disappears, 

 and then the conjugation-canal gradually becomes thicker and 

 thicker, more of the body-substance from both sides passing 

 into it (fig. 9). Although the cytoplasm of the two animals 

 is in this way very intimately mixed in the canal, the dis- 

 tinctness of the individualities is not effaced. We recognize 

 this from tlie fact that on the least disquietude the cell-bodies 

 separate from each other in the middle of the canal, and lie 

 towards each other covered by a thin membrane. As slight 

 disturbances of the conjugated Asellicolce are almost inevitable 

 in the separation of the gill-laminse, the observer very fre- 

 quently finds in the middle of the canal a perpendicular or 

 somewhat oblique partition-wall (fig. 9), which consists of 

 these two membranous layers pressed together; it disappears 

 again when the pair is placed under favourable conditions. 



When the bridge of union has grown, in the manner 

 A7in. & Mag. N. Hist. Ser. 6. Vol ii. 15 



