88 THE INVERTEBRATA 



mammalian host, where they give rise to trophozoites which infest 

 the red corpuscles. 



Three species of Plasmodium infest man — P. vivax which sets free 

 a generation of schizozoites in forty-eight hours, P. malariae which 

 does so in seventy-two hours, and P. falciparum whose schizogony 

 occurs at more irregular intervals. Since the attacks of fever take place 

 when the corpuscles break up and set free the toxins formed by the 

 parasites, the fever caused by P. vivax returns every third day and is 

 known as ''tertian ague", and that caused by P. malariae ("quartan 

 ague ") recurs every fourth day, while P. falciparum causes irregular 

 (quotidian) fevers which are more or less continuous. These latter 

 are the "pernicious malaria" of the tropics. The morphological 

 differences between the species are small, but P. vivax is distinguished 

 by the active movement of its pigment granules and the large number 

 (15-24) of its schizozoites, P. malariae by the sluggishness and often 

 quadrilateral form of its amoeboid stage, P. falciparum by the paucity 

 of its pigment and by its curved, sausage-shaped gamonts. 



Piroplasma (= Babesia). Organisms of doubtful affinity, possibly 

 related to the Haemosporidia, which infest red corpuscles of mammals 

 and are transferred by ticks. In the corpuscles, they are unpigmented 

 bodies, round or pear-shaped according to stage, which multiply 

 usually by binary fission. Details of the stages in the tick are un- 

 certain. At least one species passes from generation to generation of 

 the tick through the ovum. Piroplasma is not found in man, but is the 

 cause of red- water fever in cattle and fevers in dogs. 



Order GREGARINIDEA 



Telosporidia in which the adult trophozoite becomes extracellular; 

 and the female (as well as the male) gametes are merogametes. 



Intestinal and coelomic parasites of invertebrates, especially of 

 arthropods and annelids. 



Suborder SCHIZOGREGARINARIA 

 Gregarinidea which undergo schizogony. 



Schizocystis (Fig. 76). Parasitic in the intestine of the larvae of 

 dipterous flies. The young trophozoite attaches by one end to the gut 

 epithelium of the host. Its nuclei multiply. When ripe it undergoes 

 multiple fission. The products (schizozoites) either repeat asexual 

 reproduction or become gamonts. These undergo syzygy, coencyst- 

 ment, and gamogony. The gametes unite, and the zygotes form small 

 oocysts (" spore cases ") within the gamocyst. In its case each zygote 

 divides into a bundle of sporozoites. The spores are set free and 



