264 THE MICROSCOPE. 



There is no contractile space, the sole ordinary mani- 

 festation of vitality consisting in an incessant change 

 of form, without the elongated pseudopodia of the Amoeba 

 being ever thrust out. The mechanism of the nutritive 

 act is, in a general sense, the same in this unicellular 

 Protozoa as in a simple celL In the Greg&rince 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, Actinopkrys, 

 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 absorption 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 gelatine attracts water. 

 Tissue, distinguished by the same character, prevails 

 throughout the entire class of the Entozoa. The Gregarina 

 inhabit the intestines of invertebrate animals, insects, 

 worms, molluscs, &c. but have not been discovered in the 

 alimentary canal or other organs of the Vertebrata. In 

 this class they appear to be represented, however, by 

 very closely allied organisms, the Psorospermice. Miiller 

 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 generally of a cylindrical or some- 

 what 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 occa- 

 sionally 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 history of these minute parasites, 

 are well worthy of investigation. 



