172 MICROSCOPIC FAUNA. 



1865, by Prof. H. J. Clark, the basal adherent apparatus is 

 described. It appears that they reproduce by gemmation. The 

 T. pediculus does not apparently injure its host, and makes use of 

 him only for locomotion. 



There is a second infusorial guest which the Hydra often 

 entertains, the Kerona polyporum, see Plate XII., Fig. 4. When 

 the two abound, it may not be unfrequently observed that the 

 Trichodinae mount on the backs of their companions, and thus 

 utilise them for the enjoyment of locomotion without having to exert 

 themselves. According to Ehrenberg, the Keronse, of which there 

 seems to be but one species, are animalcules, free swimming, 

 persistent in shape, flattened or piano convex, subreniform, 

 possessing no true frontal, ventral, or anal styles ; but in place of 

 these several arcuate rows of short ventral setae, and other longer 

 setae, forming a continuous fringe round the peripheral border. 

 Length of this species a one-hundred and ninetieth to a one- 

 hundred and twenty-sixth of inch. It is found in fresh water, on the 

 surface of the fresh-water polypes. Hydra fusca and H. vulgaris, 

 and on those creatures in company with Trichodina pediculus. 

 It was originally premised that this species preyed upon the living 

 tissues of the polype, which serves it as an host, the characteristic 

 thread-cells of the higher organism being frequently found inside 

 it. Such structures, however, are only incepted with other waste 

 matter thrown off from the surface of the polype's integument, 

 and in the removal of which its tiny guest plays the role of a 

 useful scavenger. Other food matters, such as monads, desmids, 

 and diatoms, are devoured with equal avidity, and form an impor- 

 tant addendum to its customary bill of fare. 



Among the Entomostraca, which inhabit our canal, we find 

 of course Daphniadse. The Daphnia pulex is well known, and 

 must be familiar to all. There are seven species of Daphniadae. 



1. Daphnia piilex the best known. 



2. D. psittacea. — Chiefly distinguished by a long serrated, sharp 

 spine on the posterior angle of the shell, which character it also 

 possesses with the next. 



3. D. Schoifferi. — This species is, however, distinguished from 

 the former by the smallness of its head, and the fine reticulations 

 on its shell. 



