616 THE AMERICAN NATURALIST. [Vou. XXXIX. 
and encystment follows fertilization. The attempts to homolo- 
gize these two methods are not wholly satisfactory, and do not 
shed much light on the relationship of the two groups. It may 
be observed, however, that wherein the Coccidia differ from the 
gregarines, they approach the conditions found in the highest - 
animals. 
Accordingly, in the attempt to derive the Coccidia from the 
gregarines, it is advisable to seek evidence other than that fur- 
nished by the reproductive processes. This is furnished by the 
life history and the habitat. The Coccidia display an alterna- 
tion of generations and live within cells. These are both indic- 
ative of a greater specialization than is shown by the gregarines. 
We may imagine that in evolution certain sporozoites penetrated 
completely within the cells of the intestinal epithelium, and there 
remained and developed. Such a habit, once acquired, would 
speedily lead to morphological degradation. The Polycystidea 
may almost be said to lead a free life. They possess and exert 
the power to move from place to place. But the Coccidia, living 
within cells, add to the degradation which follows from a para- 
sitic, that which results from a sedentary habit. Two influences 
are thus at work upon them, and they have become the most 
simply organized of all the Sporozoa. Their form is spherical or 
ellipsoidal, that taken by any non-living liquid when in a state 
of equilibrium. Anatomically, they are merely nucleated masses 
ef cytoplasm, not even displaying differentiation into ectosarc 
and endosarc. 
It then seems justifiable to derive the Coccidia from the Poly-. 
cystidia, although perhaps indirectly, for reasons which I shall 
give. The fact that some inhabit the internal organs of the 
host presents no difficulty. In numbers, those infesting the 
intestinal epithelium are much in excess. These were doubtless 
first evolved. The intracellular habit once acquired, the organ- 
infesting Coccidia could easily have arisen from those living in 
the intestinal epithelium. The more venturesome sporozoites, 
by passing entirely through the intestinal wall, finally gained one 
of the internal organs. The pabulum furnished by a kidney or 
testis cell being satisfactory, the line was established. 
The last group of the Telosporidia is the Haemosporidia. 
