216 Dr. L. Plate on Asellicola digitata. 



are generally placed somewhat obliquely and unsymmetrically, 

 not running exactly parallel to the outer margin. One pole 

 of the long axis of the swarmer is almost always somewhat 

 altered by the constriction separating it from the parent ; it 

 has a small pit or a short tubercle. At this end of the body 

 the bands of cilia of the two sides do not pass into each other, 

 but they are interrupted for a small space. In the interior of 

 the swarmer there are a nucleus of elongated or irregular 

 form, a contractile vacuole, and not unfrequently those green 

 grains and " Tinctinkorper " which I have already mentioned. 

 The animalcules swim about irregularly, and immediately 

 attach themselves when they have found a suitable dwelling- 

 place. They almost exactly resemble the buds of Dendro- 

 cometes paradoxus, and really differ from them only in this 

 point, that the circlets of cilia advance more towards the centre 

 of the under surface, while in the latter Acineta they are 

 seated quite at the outer margin. They also agree in that 

 sometimes the ventral surface is nearly as convex as the 

 superior surface. 



When the swarm-bud has attached itself it loses its cilia in 

 some manner not exactly ascertained and passes directly into 

 the form of the old animal by pushing out delicate tentacles. 

 It is remarkable that the nucleus of individuals which, 

 judging from their size, have not long assumed the sessile 

 mode of life, not unfrequently shows an exceedingly sharp 

 longitudinal striation. This arrangement of the chromatic 

 elements in the nucleus seems subsequently to give place 

 again to the ordinary form of a fine mesh work ; at least I 

 never observed it in old specimens. I have not found it also 

 in the nuclei of the swarm-buds. I must leave it undecided 

 why this structure occurs ; but it is certain that it is not con- 

 nected with the divisional phenomena of the Acineta. 



When Dendrocometes paradoxus is compelled to seek a new 

 dwelling by the change of skin of the gill- lamina, it exhibits, 

 as I have already indicated, a very peculiar behaviour. 

 It passes through all the stages of bud-formation and becomes 

 converted, with the loss of the basal membrane and of a small 

 vesicle of plasmatic substance, into an embryo which is 

 nearly as large as the parent-animal. The same phenomenon 

 occurs also in Asellicola, so that on gill-plates of which the 

 cuticle has lifted a little we not unfrequently find all the indi- 

 viduals apparently engaged in reproduction. The only diffe- 

 rence is (? always) that the whole of the plasma of the mother 

 passes into the body of the swarmer without leaving behind 

 any residual substance. 



The most interesting part of the biology of Asellicola digi- 



