Hi/datinaea.'] infusorial animalcules. 625 



The lobes of the rotatory organ of F. cornuta resemble very much 

 those of F. ornata : only five exist, while in the other there are six, 

 according to Ehrenberg. The F. camimnulata is gregarious, but F. 

 cornuta solitary ; and the former, too, is stronger and more active 

 than the latter. 



Family.— HYDATINAEA. 



The members of this highly-organized and extensive family of 

 rotatory animalcules are destitute of lorica; their wheel-like apparatus 

 is divided into several distinct lobes or parts, always more than two 

 in number. The compound state of this organ is best expressed by 

 saying that it is not a mere circular or semi-circular row of cilia, 

 but several groups, completely separated from each other, and 

 situated on the anterior part of these soft-bodied animalcules. All 

 the genera, Polyarihra excepted, have a tail-like foot, or a styliform 

 or pincer-formed process on the abdominal surface — hence not 

 properly a tail, that member being always a prolongation of the 

 dorsal surface. In several of the genera, the muscles for altering 

 the form of the body are distinct. The nutritive system is com- 

 pletely elicited in all ; it consists mostly of a simple conical 

 alimentary canal, without a stomach-like division (Coelogastrica) ; 

 but Diglena catellina, Polyarthi'a, and Triarthra longiseta, have 

 true constricted stomachs. Enteroplea, Notommata myrmeleo, N. 

 syrinx, N. clavulata, the Synchaetae, and Diglena lacusiris, have a 

 long oesophagus or stomach, and a suddenly-attenuated discharging 

 canal (Gasterodela). Enteroplea alone has radiant vessels at the 

 oesophagus. Notommata clavulata and Diglena lacustris have 

 special caeca at the stomach. Enteroplea is the only genus destitute 

 of teeth, though their presence is doubtful in Jtattulus. Pancreatic 

 glands, under diiferent modifications, are present in all the genera. 

 The propagative system is distinctly hermaphroditic in fifteen 

 genera. The ovarium, which only evolves a few large ova at a time, 

 is mostly ovate : in Notommata myrmeleo, in N. clavulata, and so also 

 in Diglena lacustris, it is very long. It communicates, by a short 

 oviduct, with the alimentary canal near its termination. None of 

 the species are viviparous. There are two filiform, extended, wedge- 



