PLASMODIUM 



125 



the gut. They feed by absorbing diffusible food-stuffs, such 

 as peptones and carbohydrates, from their hosts, and store 

 up glycogen within themselves. In many the size is about 

 one-tenth of an inch. There is a firm cuticle of " proto- 

 elastin," which grows inwards so as to divide the cell into 

 a larger nucleated posterior region and a smaller anterior 

 region, and also, in the young stage, forms a small anterior 

 cap. The cell substance is divided into a firmer cortical 

 layer and a more fluid central substance. 

 The protoplasm often presents a delicate 

 fibrillar appearance, suggesting that of 

 striated muscle. The nucleus is very dis- 

 tinct, but there are no vacuoles. We may 

 associate the absence of locomotor pro- 

 cesses, " mouth," and contractile vacuoles, 

 as well as the thickness of the cuticle and 

 the general passivity, with the parasitic 

 habit of the Gregarines. 



The young Gregarine is parasitic in one 

 of the hning cells of the gut ; it grows, and, 

 leaving the cell, remains for a time still 

 attached to it by the cap (Fig. 56, «, b, c) ; 

 later this is cast off, and the individual be- 

 comes free in the gut, w^hile still increasing 

 in size. Two or more individuals attach 

 themselves together end to end, but the 

 meaning of this is obscure. Encystation 

 occurs, involving a single unit or two to- 

 gether. The details of spore-formation are 

 similar to those in Monocystis. Eventually 

 the cyst bursts, the spore-cases are liber- 

 ated, and from within each of these eight 

 spores emerge to become cellular parasites. 

 G. {Porospora) gigantea is sometimes three-quarters of an 

 inch in length — enormous for a Protozoon. 



to 



Fig. 57. — End- 

 to-end union of 

 Gregarines. — 

 After Frenzel. 



The adult of 



Eighth Type of Protozoa — Plasmodium vivax 



Plasmodium, one of the Haemosporidia, is parasitic in 

 the red blood cells of man and other Vertebrates. P. vivax 

 benign tertian " malaria in man. The Hfe- 



causes 



