620 THE AMERICAN NATURALIST. (VoL. XXXIX. 
E ‘ 
Organ-infesting 
Coccidia 


Acystosporea 
Intestinal 
Haemosporea Coccidia Monocystidea 
| 
m 
Polycystidea 
The habitat of the Polycystidea, the intestine of their hosts, 
has enabled them to lead a practically free life. Accordingly, 
they are the least modified of all Sporozoa, and have retained 
nearly as complex an organization as the Flagellates. They have 
given rise, on the one side, to the Monocystidea and on the other 
to the Coccidiomorpha. The former followed much the same 
lines as their immediate ancestors, but have undergone morpho- 
. logical degradation. The Coccidiomorpha became adapted to an 
intracellular life, and separated into two groups. In one of 
these, the inert Coccidia, morphological degradation has been 
carried to its extreme. The greater anatomical complexity of 
the Hzemosporea is to be credited to their habitat. The liquid 
blood offers a radically different environment from the motion- 
less epithelium. In consequence, the power to move, possessed 
at the outset by the Haemosporea as an inheritance from their 
Polycystid ancestors, has not been lost. Thus these animals 
possess the characteristic Telosporidian organ of movement, a 
myocyte. The Acystosporidia, further evolved, have apparently 
lost the ability to move from place to place. Their inertness, 
although comparable to that of the Coccidia, has been independ- 
ently acquired. Finally, in their ability to display amoeboid 
movements, they have not sunk quite so low. 
Mesnil! considers the ancestral Telosporidian to be a Mono- 
cystid intestinal gregarine. Minchin derives the group from a 
hypothetical intracellular form. In both cases this ancestor is 
supposed to have given rise to existing gregarines on the one 
hand, and to the Coccidiomorpha on the other. To my mind, 
1 Vol. Jubil. Soc. de Biol., Paris, 1899. 
