PROTOZOA. GREGARIN^E. 371 



double cone, like that presented by some species of 

 Diatomacese, whence their name pseudo-naviculae. At 

 length the cyst contains nothing but pseudo-naviculae, 

 sometimes enclosing granules, which gradually disappear, 

 and finally the cyst bursts. Encystation seems to take 

 place much more rarely among the bilocular forms of 

 Gregarinae than in the unilocular species found in the 

 earthworm and other Annelids." 



In the Gregarince the food is taken in indiscriminately 

 at every point of the surface of the body by imbibition. 

 The food most likely is in the fluid state. In Spongilla, 

 also, this is probably the case. But it is generally agreed 

 that in Amoeba, Actinophrys, and agastric Infusoria, only 

 solid alimentary particles are taken as food. The simplest 

 animal is indeed far more complex than is implied in the 

 word unicellular, and it can be clearly proved that there 

 are few points in common between a simple cell and a so- 

 called unicellular protozoon. The system of contractile 

 vesicles and dependent sinuses, so general in the least 

 organized protozoon, is unknown in the history of cells. 

 Fluid absoption by the surface is the normal method of 

 feeding in these low types of animal life. This absorptive 

 faculty is an inherent property of the substance of which 

 they are composed. It attracts certain aliments, as gela- 

 tine attracts water. Tissue, distinguished by the same 

 character, prevails throughout the entire class of the Pro- 

 tozoa. Although the Gregarince mostly inhabit the intes- 

 tines of invertebrate animals, they are often found in the 

 alimentary canal of the Vertebrata. In this class they 

 appear to be represented, however, by very closely allied 

 organisms, the Psorospermice. Mu'ller gave this last- 

 mentioned name to some very singular minute bodies he 

 discovered within sacs upon the skin and gills, and in the 

 internal organs, of many fishes. These animals are gene- 

 rally of a cylindrical or somewhat elliptical form, although 

 sometimes a sort of head appears to be produced by the 

 constriction of the anterior extremity of the body, and 

 this head-like portion is occasionally furnished with a 

 curious soft process and lobes. They are very sluggish in 

 their movements, although a few possess true cilia. Their 

 curious mode of development, with other points in the 



BB 2 



