350 DESCRIPTION OP [Rotatoria. 



FAMILY XXVII. HYDATINAEA. 



The members of this highly-organized and extensive 

 family of rotatory animalcules are destitute of lorica ; they 

 possess a wheel-like apparatus, or vibratile organ, divided 

 into several distinct series or parts, always more than two 

 in number. The compound state of this organ is best ex- 

 pressed by saying that it is not a mere circular or semi- 

 circular row of cilii, but several rows or groups, completely 

 separate from each other. They are situated on the an- 

 terior part of these soft-bodied animalcules. All the 

 genera, Polyarthra excepted, have a tail-like foot, or a 

 styliform or pincer-formed process, on the abdomen hence 

 not properly a tail, that member being always a pro- 

 longation of the dorsal surface. In several of the genera, 

 the muscles for altering the form of the body are distinct. 

 The nutritive system is completely elicited in all ; it con- 

 sists mostly of a simple conical tube for the alimentary 

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

 but Diglena catellina, Polyarthra, and Triarthra longiseta, 

 have true constricted stomachs. Enteroplea, Notommata 

 myrmeleo, syrinx, clavulata, the Synch aetae, and Diglena 

 lacustris, 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 

 coeca at the stomach. Enteroplea is the only genus 

 destitute of teeth, though doubtful in Rattulus. Pancreatic 

 glands, under different modifications, are present in all the 



