122 SOME MINUTE ANIMAL PARASITES 



zoites within each spore twist until they lie parallel, 

 in the position easiest for emergence, and when they 

 escape, they glide away with sinuous undulatory 

 movements over the intestinal surface. Each tiny 

 germ (Figs. 27, spz. ; 28, A ) is extraordinarily active, 

 and is aided in its movements by manufacturing 

 a surface for its own evolutions, by secreting a 

 gelatinous substance which provides it with a slip- 

 pery surface on which it glides forward. Small as it 

 is, only about ^sW inch, it contains a small nucleus 

 of distinct, uniform structure. The sporozoite remains 

 free only a very short time in the lumen of the gut, 

 but rapidly attaches itself to an epithelial cell, and 

 proceeds to bore its way inwards (Fig. 27, spz.). 

 Once within, the parasite curls on itself, gradually 

 loses its elongate form, and becomes rounded (Fig. 28, 

 B t C). It grows steadily at the expense of the host 

 cell, and soon the latter becomes greatly atrophied, 

 its nucleus is much displaced, and the parasite lies 

 in a clear space within the host cell (Fig. 27, par.). 

 This passive, feeding stage of the existence of the 

 organism is known as the trophozoite (Fig. 28, D). 



Growth continues for some time, but ultimately 

 a period is reached when the parasite ceases to feed 

 and prepares to perpetuate its kind and to increase 

 its numbers within the same host. The nucleus 

 begins to separate into two portions, and no sooner 

 is the division accomplished than it is repeated until 

 eight to fourteen portions are formed (Figs. 27, 

 sch. ; 28, E). Occasionally, when there is a great 

 abundance of nourishment and much space available, 

 twenty daughter nuclei may be produced, while when 



