Dr. L. Plate on Asellicola digitata. 213 



slow process lasting several hours, and in such tentacles 

 when reduced to about half their size, I have seen the canal 

 penetrate inwards for a short distance. But when the ten- 

 tacles have become completely incorporated with the cell- 

 plasma every trace of these canals has disappeared. 



The near relationship of Asellicola to Den'drocometes, 

 which has already been repeatedly referred to, is also 

 evidenced by a careful examination of the free extremities of 

 the suckmg-tubes. If we fix one of these for a few minutes 

 in a lively specimen we observe that the extreme tip raises 

 Itself from the tentacle as a distinct tentaculet, which is con- 

 stantly (several times in a minute) pushed out and retracted 

 ihis pumping movement therefore takes place even when tiie 

 tentacle is not m a position to take up nourishment. Why it 

 occurs is hard to say. We may suppose that the animals 

 either mhaust water, which is then subsequently got rid 

 ot again through the contractile vacuole, or that we have 

 here to do with a sort of involuntary movement which is of 

 service to the individual only when by chance an Amoeba 

 an Infusonan, or some other kind of nourishment has come 

 in contact with the tentacle and remained adherino- to it In 

 opposition to this last notion it may, however, be^urged with 

 justice that the tentaculets are often only in part in activity 

 while the others on the same animal are quite quiescent ' 

 _ In the fully extended state the hinder limit of the tentaculet 

 IS scarcely recognizable. But as soon as the invagination 

 which begins at the base of the tentaculet, has commenced a 

 small cushion is produced which distinctly separates the two 

 divisions from each other and becomes more and more 

 marked m proportion as the terminal member disappears. 

 When the latter is finally completely retracted the Dad 

 appears in optical section as two shining knots situated at 

 the extremity of the tentacle. These tentaculets exactly 

 resemble the points of the fingers which occur in great num- 

 bers upon each tentacle of Dendrocometes paradoxus, only 

 hey are somewhat larger (0-0025 millim. in diametei-) and 

 therefore more easily investigated in their structure and mode 

 of action. In the last-mentioned Acineta, therefore, each 

 tentacle is apparently produced by the fusion of several ten- 

 tacles such as we meet with in Asellicola. Dendrocometes 

 also so tar represents a higher stage of difFerentiation as each 

 canal starting from a fingerlet possesses a delicate proper 

 wail, and by means of this penetrates deeply into the cell- 

 body. '' 



The tentaculets of Asellicola very probably secrete a viscid 

 substance, for I have frequently observed that very small 



