356 DESCRIPTION OF [Rotatoria. 



produced by delicate internal cilii, and must not be mis- 

 taken for the motion of Monads. 



583. Hydatina hrachydactyla. The little Ihjdatina. — 

 Body cylindrical, truncated anteriorly, and suddenly at- 

 tenuated at the base of the foot; claws short. Found on 

 Hottonia, &c. Length l-144th. 



Genus CLI. Pleurotrocha. The awl-shaped tooth 

 Rotatoria have no eyes, but possess a single tooth in each 

 jaw, and a furcated foot. The rotatory organ consists, not 

 of a simple wreath of cilii, but of cilii distributed in 

 bundles near each other, the bundles being placed in mus- 

 cular cases. In P. gibba there are two muscles for 

 moving the foot, and in all the species the cesophagal head 

 has four. This head is globular, it has two single-toothed 

 jaws (Jig. 396); these, and the short oesophagus, the simple 

 conical alimentary canal, having anteriorly two spherical 

 pancreatic glands, constitute the nutritive apparatus. The 

 posterior opening of the canal is at the base of the foot, 

 upon the dorsal surface. The propagative system consists 

 of a globular ovarium. In P. leptura a contractile vesicle 

 is seen. Organs of sensation are not satisfactorily known, 

 and the nervous loop in the neck of the Hydatina appears 

 wanting in this genus. 



584. Pleurotrocha gibba. The thickened Pleurotro- 

 cha. — Body truncated anteriorly, enlarging from the front 

 towards the base of the foot, where it is suddenly attenu- 

 ated, the toes, or claws, short and turgid ; near the mouth 

 is a beak-like projection, forming an under lip. Fig. 395 

 is a right side view, and Jig. 396 the teeth and cesophagal 

 head dissected out. Found with Hydatina hrachydactyla. 

 Length 1-2 16th. 



