Sydatinaea.'] infttsobiai. animalcules. 641 



Genus PoLYARTHRA. The many-finned Rotatoria have a single 

 cervical eye, no foot, bnt are pro^•icled with cirrhi, or pectoral fins ; 

 the rotatory organ consists of four bundles of cilia, inserted in as 

 many muscvilar sheaths ; they sometimes appear like the double 

 rotatoiy organ of a Bracltionus, and the form of the body resembles 

 Anurm ; but it is, howevQi', soft, and the rotatory organ double ; 

 laterally, two longitudinal dorsal muscles arc known ; the frontal 

 region has little horns, provided with biistles, and upon the breast 

 six strong styles, or barbs, forming two clusters, which move in a 

 fin-like manner. The system of nutrition consists of an oesophageal 

 head, having two single- toothed jaws, a short oesophagus, an 

 alimentary canal, with a stomach-like division, produced by a con- 

 striction, and two pancreatic glands. An ovarium exists in both 

 species, and in one of them a contractile vesicle ; nothing is kno\vn 

 of the vascular system, unless the two soft horns at the brow arc 

 respiratory tubes ; a large frontal ganglion, and a round red eye, 

 indicate the system of sensation. 



The preceding genera of this family Hydatincea, form, together 

 ^vith two peculiar to himself, viz., Playiognatha and Zindia, in the 

 system of Dujardin, the family Flosculan'cns ; but this genus Poly- 

 arthra, and a few others in this familj' of Ehrenberg, belong to the 

 BracMoniens of the above-named author. 



From the remarks of the French naturalist, it is to be infei'red 

 that he regards the distinction between Polyarthra and Triarthra, as 

 insufficient to characterize them generically. 



P. trigla. — Body oval, almost square, having six setaceous pinnoe. 

 It swims quickly, and often leaps, like the water-iiea ; this last 

 motion is produced by the fins, or pinnaj, the former by tlie ■\ibi'atile 

 organs. Fig. 425 represents the imder side, while the animalcule is 

 swimming, with the pinnae depressed ; fig. 400 a dorsal view, while 

 leaping, or springing; and fig. 401 a side \dcw (right.) This crea- 

 ture is infested with Colacium. Found amongst Conferva. (l-140th.) 



P. platyptera. — ^Body oval, almost square, with six serrated broad 

 sword-shaped pinnae. It is represented at fig. 402. Foimd amongst 

 Chlamidotnonas. Length l-190th. 



Genus DiGLEXA (?). The tuo-eycd Rotatoria. — Eyes two, frontal ; 

 foot forked. Excepting the foot, and rotatory organ, they have no 



