184 DESCEIPTION OF Poly gastric a."] 



generic characters, -^'hioh he would donve from the nature or appa- 

 rent structure of the integumeut, and the number or mode of insertion 

 of the filaments. He thus forms a genus Polyselmis, characterized by 

 its many filaments ; two genera Zygoselmis and Keteronema, by a pair 

 of filaments, in the foraier of equal, in the latter of unequal size. 

 The remaining Euglenea have hut a single filament, and can be but 

 uncertainly defined ; such are the Eugleneoi mostly coloured, and 

 having a red eye speck, and with a tail ; the Astasia without colour 

 and tail, but with a filament flexible throughout, and springing 

 abruptly from a notch in the anterior estremitj' ; and the Peranema 

 differing from the Astasia, only in having a filament rigid at the 

 base, and apparently but a continuation of the tapering anterior 

 extremity of the animalcule. The two last genera, are, however 

 but provisional. 



Dujardin difiers entirely from Ehrenberg, in his interpretation of 

 the internal organization of the Astasia or Eiiglenians ; neither 

 stomachs, sexual system, ova, or nerve matter are recognized by 

 the former. 



The members of this family mostly inhabit stagnant ponds. 

 I have always foxind them at the surface. They sometimes tinge 

 the water with their own colovir. "When swimming they present an 

 elongated form, but when fixed, often appear as round globules. 

 They seem capable of progressing, by alternately fixing and ad- 

 vancing the head and tail after the manner of a leech; Dujardin 

 doubts the oblique fission of Chlorogonium. 



It is with certain members of this family that M. Thuret finds so close 

 an afiixity — even an apparent identity, to exist with the reproductive 

 spores — Zoospore of the Algae. "This affuiity," he says, is exhibited in 

 colour, form, number and character of the ciliaiy filaments, in the 

 contents, not excepting the coloured eye-speck, in the mode of self- 

 fission, and also in the power of locomotion. "What is still more, 

 both Zoospores and Astasicca tend to the light, disengage a gas, most 

 probably oxygen, and emit a peculiar spermatic odour. However, 

 by continued watchiag the Zoospores are seen to affix themselves 

 to some body, surrender theii' seeming animal hfe, and proceed to 

 germinate, developing a tissue similar to that of the plant which 

 gave them bu'th. On the other hand, the true Astasicea, if they 



