Dr. L. Plate on Asellicola digitata. 209 



Infusoria *. When he discovered the Asellicola Stein erro- 

 neously regarded the Acineta as developmental states of the 

 Ciliated Infusoria, and gave our animal provisionally only 

 the designation of the " fingered Acineta," as he had not yet 

 found the ciliated form belonging to it 5 he seems also not to 

 have studied it thoroughly, as in his description he mentions 

 only the general form of the body, without entering into 

 details as to the structure of the tentacles, the nature of the 

 nucleus and of the interior of the cell, the reproduction, and 

 the conjugation f. 



Asellicola digitata (PI. X., B. fig. 4) is a non-pedunculate 

 hemispherical Acineta furnished with a nucleus (N) and con- 

 tractile vacuole {cv.), and which adheres closely to the surface 

 of the gill-lamina by its flattened but gently rounded under 

 surface. It attains a maximum length of about O'll millim, 

 and an elevation of 0*06 millim. The whole body is covered 

 with a thin cuticle, which nevertheless appears to have a double 

 contour and is continued over the numerous tentacles {t) 

 which radiate from the dorsal surface and in form and 

 grouping are very characteristic of our species. The cuticle 

 is of equal thickness and colourless over tlie whole of the body 

 proper, except that on the underside it forms in the middle 

 an elliptical thickened ring (r), which rises above the basal 

 surface, and by means of which the animal is attached to its 

 point of support. Of course, as in all Suctoria, the form of 

 the body is liable to small deviations, some of which the 

 reader will find figured by Stein \. The outlines of the body 

 may also be altered by reagents. While in living individuals 

 the basal surface is always closely applied to the branchial 

 lamina, it swells into a hemispherical convexity when the 

 animals have died in the water, and it is then seen very clearly 

 that the Asellicola only adheres by the above-mentioned ring. 

 The same result may be attained by means of acetic acid and 

 other agents which produce a swelling of the plasma. 



While Dendrocometes ^paradoxus attaches itself but rarely 

 to the margin of the gill-laminse of Gammarus pulex^ and is 

 generally met with on the actual surface of the plate, Aselli- 

 cola digitata acts just in the contrary way. The individuals 



• F. Stein, ' Die Infusionsthiere auf ihre Entwicklungsgeschichte un- 

 tersuclit,' Leipzig, 1854, p. 228. 



t Claparede and Lachmann (' Etudes sur les Infusoires, &c.' i. p. 386) 

 and S. Kent (' Manual of the Infusoria,' ii. p. 812), as I now find, place 

 the Aselliculd in the genus Trichophrya, without, however, supporting 

 Ihis view by their own observations; but T. epistylidis differs so much, 

 especially in the structure of the tentacles, from the " gefingerte Acinete," 

 that a new genus must unquestionably be established for the latter, 



X Loc. iit. Taf. V. iigs. 19-22. 



