174 DESCRIPTION OF {Pohjgastrica. 



sided figure, while in the non-siliceous they are generally 

 flat, with three to five sides. 



Of the internal organization of these creatures little is 

 known, owing to their opacity, and the structure of the 

 enveloping lorica. In many, however, large transparent 

 variable vesicles are seen among the mass of coloured 

 granules which occupy the greater part of the lorica. 

 These vesicles are considered by Ehrenberg to be diges- 

 tive cells, and the coloured mass ova, while the latter is 

 the Chloriphylle of botanists. In some species, as soon as 

 the coloured ova is protruded the parent dies ; in others, 

 the ova form a Monad-like mass, and when matured the 

 parent separates from it; hence, says Ehrenberg, has 

 arisen the opinion of the transition of animals into plants. 

 In Microsterias, Arthrodesmus, and one or two other 

 genera, says Dr. Ehrenberg, male reproductive structures 

 are visible, but no trace of a sensitive system has been 

 discovered. 



From the clustering nature of this sluggish family, and 

 the rigidity of their coverings, they resemble the confer- 

 void Algae, and other minute vegetable forms, and are hence 

 confounded with them ; but in their mode of propagation 

 a distinction may be recognised. In the Bacillaria, the 

 self- division is always longitudinal, so that the conferva- 

 like forms are not composed of long slender and filiform 

 bodies, like plants, but of short and broad filiform portions. 

 Sometimes the self-division is from back to front, or from 

 side to side; the single creatures are then band-like or 

 half-moon- shaped. 



In Acinata, organs of locomotion are visible, as feelers ; 

 but these creatures deviate so much from the Bacillaria in 



