28 ANIMAL STUDIES 



are growing together they appear like a delicate growth 

 of mold upon the water weed. The stalk is peculiar in 

 "being traversed by a muscle fiber arranged in a loose spiral, 

 which, upon any unusual disturbance, contracts together 

 with the body into the form shown in Fig. 10, b. 



These few examples serve to show the general plan of 

 organization and the method of locomotion of the Infuso- 

 ria ; but, as upward of a thousand species exist, with widely 

 differing habits, many interesting modifications are present. 

 Some have been driven in past time to adopt a parasitic 

 mode of life within the bodies of other animals. At pres- 

 ent they are devoid of locomotor organs, and as they absorb 

 nutritive fluids through the surface of the body all traces 

 of a mouth are also absent. The reproductive processes 

 also are peculiar, but they do not concern us now. 



29. Gregarina. Another type of protozoan worthy of 

 special attention is that of the Gregarina (Fig. 11), various 

 species of which live in the alimentary canal * of crayfishes 

 and centipeds and certain insects. Gregarina is a parasite, 

 living at the expense of the host in whose body it lies. It 

 has no need to swim about quickly, and hence has no swim- 

 ming cilia like Paramcecium and the young Vorticella. It 

 does need to cling to the inner wall of the alimentary canal 

 of its host, and the body of some species is provided with 

 hooks for that purpose. The food of Gregarina is the 

 liquid food of the host as it exists in the intestine, and 

 which is simply absorbed anywhere through the surface of 

 the body of the parasite. There is no mouth opening nor 



* Specimens of Gregarina can be abundantly found in the alimen- 

 tary canal of meal worms, the larvae of the black beetle (Tenebrio moli- 

 tor), common in granaries, mills, and brans. " Snip off with small 

 scissors both ends of a larva, seize the protruding (white) intestine with 

 forceps, draw it out, and tease a portion in normal salt solution (water 

 will do) on a slide. Cover, find with the low power (minute, oblong, 

 transparent bodies), and study with any higher objective to suit." 



MURBACH. 



