182 DEscBiPTiox OF [Poli/gastrica. 



hurst, and allow the molecules to escape". — The following arc Mr. 

 D.'s reasons for classing the Closterina with animals : — 



" 1st. That while Closterkmi has a circulation of molecules greatly 

 resembling that of plants, it has also a definite organ, unknown in 

 the vegetable world, in which the active molecules appear to enjoy 

 an uadepcndcnt motion, and the parieties of which appear capable of 

 contracting upon its contents. 



" 2ndly. That the green gelatinous body is contained in a mem- 

 branous envelope, which, while it is elastic, contracts also upon the 

 action of certain re-agents, whose effects cannot be considered purely 

 chemical. 



" 3rdly. The comparison of the supposed ova with the cytoblasts 

 and cells of plants precludes the possibility of our considering them 

 as the latter, while the appearance of a vitelline nucleus, transparent 

 but molecular fluid, a chorion or shell, deteiTnines them as animal 

 ova. It was shown to be impossible that these eggs had been de- 

 posited ia the empty shell by other infusoria, or that they were the 

 produce of some entozoon. 



"4thly. That while it was impossible to determine whether the 

 vague motions of Closterium were voluntarj^ or not, yet the idea the 

 author had fonned of a suctorial apparatus forbad his classing them 

 with plants. 



" Lastly, in no instance had the action of iodine produced its 

 ordinary effects upon starch or vegetable matter, hy coloiu'ing it violet 

 or blue, although Meyen asserts it did in his trials." 



The author therefore concluded that Closterium must still be 

 retained as an iniusory animal, although it is more than doubtful 

 whether it ought to rank with the polygastric families. 



Family.— ASTASIAEA. 



This family is characterized by its members being polygastric, and 

 deficient of the true alimentary canal, appendages, and lorica. They 

 are furnished with a single aperture, and often with a tail, and have 

 the power of changing their form at pleasure. They afford as beau- 

 tiful living bjects for the microscope as any that have ever fallen 



