No. 465.) ZWTERRELA TIONSHIPS OF SPOROZOA. 619 
evolution when the Acystosporea could infect their vertebrate 
hosts in two ways, but the intestinal method is now lost. The . 
acquisition of an intermediate host is obviously advantageous to 
the species, tending, as it does, to a wider distribution. 
There are, however, anatomical differences between the 
Hzemosporea and the Acystosporea. The former, in the troph- 
ozoite stage, possess a definite body form, on which account 
they are often spoken of as Haemogregarines. This definite 
form is due to the presence of a dense hyaline ectosarc, in 
which myocyte fibrille have been demonstrated. These ani- 
mals, although typically cell parasites, indulge in frequent 
migrations in the blood plasma, and during such “free” phases, 
they display both contractile and locomotor movements. On 
the other hand, the trophozoites of the Acystosporea appear 
never to migrate. The blood cell originally attacked is aban- 
doned only after the organism has divided by schizogony. No 
special anatomical differentiation appears to have been described, 
but the trophozoites undergo sluggish amoeboid movements. 
Accordingly, as regards both the morphology and the life 
history, the Acystosporea are clearly the more specialized 
group. It next remains to relate the blood parasites with their 
closest relatives, the Coccidia. : 
As regards the life history, the parallelism is exact, except for 
the acquisition of an intermediate host in the Acystosporea. 
The sexual processes are practically identical. Morphologically, 
however, the Coccidia are practically on a par with the Acysto- 
sporea and considerably more degraded than the Haemosporea. 
Comparing the Coccidia and the Haemosporea, the former would, 
according to our criteria, be the derived group. But the favored 
habitat of the Coccidia is the epithelium of the intestine, and it 
seems as if this must have been occupied by Sporozoan parasites 
before invasion of the blood. 
The view advanced by Minchin seems best to fit the case. 
This is that both Coccidia and Haemosporidia have arisen from 
common ancestors. These ancestors in their turn I believe to 
have been derived from the Polycystidea, and my conception of 
the interrelationships of the Telosporidia is indicated by the 
following scheme : — 
