182 KHIZOPODA. 



the members of this group ; the Infusoria, on the other hand, possess 

 a permanent locomotor apparatus in the form of cilia ; and the Gre- 

 garinida glide forwards in a more worm-like fashion by the contraction 

 of their larger body-mass. Further, the Rhizopoda and Infusoria feed 

 on solid, or at least somewhat firm food, which either (Rhizopoda) 

 simply sinks into the protoplasm, or is ingested by means of a special 

 mouth (Infusoria), while the Gregarinida are supplied with fluid food 

 exclusively by endosmosis through the enveloping cuticle. The Gre- 

 garinida live wholly as parasites, and therefore in conditions which 

 render the presence of either a temporary or permanent mouth un- 

 necessary. It is equally intelligible that the mouth is, as we shall 

 see, wanting even in some parasitic Infusoria (species of Opalina). 



The term Gregarinida must, however, be restricted to those forms 

 which are found usually in crowds in the alimentary canal or other 

 viscera of some lower animals, especially insects arid worms, and which 

 have at the first glance a superficial resemblance to microscopic Nema- 

 todes, as which indeed they were formerly described. The name can- 

 not be extended to allied organisms found parasitic on higher animals, 

 for these differ in many ways from the true Gregarines, both in ap- 

 pearance and in life-history, though closely linked to them by the 

 very characteristic reproduction by hard -shelled germs (the so- 

 called " Pseudonavicelhe," or " Psorospermiae "). I will therefore 

 introduce the term " Sporozoa " to denote the forms above referred to. 



All the three classes have, as the following survey will show, 

 representatives parasitic in man. 



CLASS I. RHIZOPODA. 



Protozoa, consisting of a memfoaneless mass of protoplasm, which 

 forms lobose, finger-like, or filiform, and often branched pseudopodia, 

 and taking in solid food without having a permanent mouth. Only a 

 few forms are naked, the majority 2>ossess cither a simple chitinous or a 

 hard calcareous or siliceous skeleton, which is provided with more or less 

 numerous openings for the protrusion of the pseudopodia, or may not 

 unfrequently consist simply of single needles. Reproduction takes place 

 partly by simple division, partly by actively moving germs produced 

 within the body-substance. 



In the simplest forms, the so-called " Monera," the body consists 

 of an apparently non-nucleated mass of protoplasm, without further 

 recognisable differentiation. At most, and that after rich feeding, the 

 body is seen to be studded with small granules, which are only absent 

 in the outermost portion. But as a rule, in the Rhizopoda, a distinct 



