212 Dr. L. Plate on Asellicola digitata. 



condition of the animal. In lively individuals several pulsa- 

 tions may take place in one minute, while in those which 

 have been kept for a long time in watch-glasses they are 

 repeated much more slowly. 



The cytoplasm of Asellicola shows a peculiarity which may 

 easily lead the observer astray. Above the cuticular ring 

 with which our Acineta attaches itself to its support we 

 observe a striated structure radiating like a fan in all direc- 

 tions, producing an impression as if a great number of fine 

 canals met together at this point. The individual rays are 

 directed obliquely upwards and the outer ones form an angle 

 of about 45° with the basal surface. As they may be dis- 

 tinctly traced up to the level of the nucleus, and therefore 

 pretty far into tlie interior of the cell, I at first supposed that 

 the canals which traverse the tentacles throughout their 

 length were continued to the centre of the lower surface. 

 This, however, is not the case ; the striated structure of the 

 plasma is in no way connected with the sucking-organs, but 

 has probably only the office of giving the cell-body an 

 increased degree of firmness at its point of fixation by the 

 development of rigid rods. 



The tentacles (fig. 4, t) proceeding from the dorsal surface 

 fix the interest of the observer more than any other part of 

 our Acineta. In comparison with the tentacles of the other 

 Suctoria they are remarkably broad, acutely terminating pro- 

 cesses of the body of 0'036 millim. in length on the average, 

 which are met with in very variable numbers in different 

 individuals, and may originate from any part of the dorsal 

 surface. So far as they radiate from the true back they are 

 in general quite straight, while those grouped in the neigh- 

 bourhood of the basal margin are usually gently bent upwards. 

 As regards their minute structure, they are externally clothed 

 with a thin membrane, a continuation of the cuticle of the 

 body, which becomes very delicate towards the apex. The 

 plasma of the tentacles appears quite clear, as there are none 

 of the coarser granules in it. In the middle it is traversed 

 longitudinally by a canal filled with a limpid fluid, which 

 opens at the anterior end. I could detect no special wall in 

 this canal, and therefore regard it as a simple longitudinal 

 fissure in the plasma. Owing to its great fineness it is often 

 not perceptible in the living animal, but may almost always 

 be demonstrated with certainty by means of osmic acid. 

 This canal is not continued, as is the case with the sucking- 

 tubes of most Acinetse, into the interior of the cell ; at least 

 this is never the case with fully extended tentacles. Fre- 

 quently, however, the latter are retracted into the body by a 



