ANIMAL PARASITES 77 



6. The spore in Monocystis is boat shaped and is often known 

 as a pseudonavicula. As in the Sporozoa in general, this is not 

 the infective stage; but the nucleus divides and the protoplasm 

 forms sporozoites. 



7. The sporozoites vary in number, depending upon the genus. 

 In Monocystis the longitudinal division of the spore content 

 into sporozoites can be indistinctly seen in the living spore 

 if the light is properly adjusted. After studying it in this manner, 

 examine sections of the seminal vesicles showing spores in cross 

 and longitudinal sections. Make drawings showing the sporo- 

 zoites and the granular "residual protoplasm." 



Other species of Monocystis may occur and should be figured 

 if found. A related genus, Zygocystis, has the adult tropho- 

 zoites more or less pearshaped, with frayed ends, and always 

 united in twos and threes. Very many species of Gregarinida 

 are known, of which the majority are parasitic in insects. 



Nematodes. — In the course of these studies roundworms 

 are occasionally to be found in the seminal vesicles of the earth- 

 worm. These are Discelis filaria of Dujardin, 1845, or closely 

 related species. 



References 



Cuenot, 1901. Recherches sur revolution et la conjugaison des gregarines. 

 Arch, biol, 17 (4): 581-652. 



Hesse, E., 1909. Contribution a l'etude des Monocystidees des oligo- 

 chetes. Arch. Zool. exper. (ser. 5), 3: 27-301. 



Mickel, C. E., 1925. Notes on Zygocystis cometa Stein, a gregarine parasite 

 of earthworms. Jour. Parasitology, 11: 135-139. 



Minchin, E. A., 1903. Section, Sporozoa. In Lankester, "Treatise on 

 Zoology," Part I, fascicle 2, pp. 154-164. 



Watson, Minnie E., 1916. Studies on gregarines, including twenty-one 

 new species and a synopsis of the Eugregarine records from the Myria- 

 poda, Coleoptera and Orthoptera of the World. Illinois Biol. Mono- 

 graphs, 2 (3), 258 pp. 



