50 MANUAL OF ZOOLOGY. 



The following is a tabular view of the divisions of the 

 Protozoa : 



Class I. GREGARINID^. .N, f^fo***** 



Class II. RHIZOPODA. 



Order i. Monera. 



2. Amcebea. 



., 3. Foramini-fera. 



4. Radiolaria. 



5. Spongida. 



Class III. INFUSORIA. 



i 



Order i. Suctoria. 

 2. Cilia 'ta. 

 3. Flagellata. 



3. CLASS I. GREGARINID^:. The Gregarinidce may be defined 

 as parasitic Protozoa, which are destitute of a mouth, and do not 

 possess the pofoer of emitting " psendopodia^ They constitute 

 the lowest class of the Protozoa, and comprise certain micro- 

 scopic animals which are parasitic in the alimentary canal of 

 both Invertebrate and Vertebrate animals. They have, how- 

 ever, a special liking for the intestines of certain insects, being 

 commonly found abundantly in the cockroach. As we shall 

 see hereafter, in all probability a great deal of the degraded 

 character of the Gregarinidce is due to the fact that they are 

 internal parasites, and are therefore not dependent upon their 

 own exertions for food. 



Nothing anatomically could be more simple than the struc- 

 ture of a Gregarina, since it is almost exactly that of the un- 

 impregnated ovum (fig. 2, a). An adult Gregarina, in fact, 

 may be said to be a single cell, consisting of an ill-defined 

 membraneous envelope rilled with a more or less granular 

 sarcode with fatty particles, which contains in its interior 

 a vesicular nucleus, this in turn enclosing a solid particle, or 

 nucleolus. In some the body exhibits an approach to a more 

 complex structure by the presence of internal septa ; but it is 

 doubtful whether this appearance may not be due to the appo- 

 sition and fusion of two separate individuals. A separate order, 

 however, has been founded upon individuals of this kind, under 

 the name of Dicystidea ; the name Monocystidea being retained 

 for the ordinary forms. As regards the size of the Gregarince, 

 they vary from about the size of the head of a small pin up 

 to as much as half an inch in length, when they assume the 



