The Lesser Haemosporidina *

SYNOPSIS. Although the Haemosporidina are a large group, few of them arc well known. Those considered here are called the “lesser Haemosporidina” because they have, on the whole, much less impovtance than the malaria parasites of man. They are, nevertheleq far from insignificant because some cause serious disease in the lower animals and probably play an important role in the maintenance of biological balances. Their use as research tools has also often led to very useful discoveries directly applicable to human malaria. Only four species of the 60 or so now known in the genus plasmodium parasitize man; we are still ignorant of many of the most elemental facts relating to the biology of the rest. The rectors of many remain undiscovered and, partly as a result, their exoerythrocytic stages have never been observed. Even when such knowledge cxists. there are many lacunae in what we know of thcir physioloey. A really practical method of cultivating the various stapes would be of great help. We also need much more knowledge of the close relatives of the malaria parasites, comprising the genera Hueinoprofeits , Hepatocystis , and Lertcocytoroon . There are close parallels in their host occurrence which undoubtedly have evolutionary significance. Yet such facts are difficult to interpret, although it seems likely that Haenzoproteus may be the oldest of the four. Whether Babesia and Dactylosoma should be included in the Harniosporidimz has been questioned. It is the author's opinion that it would be better to retain them. Despite important differences there are basic similarities. Much remains unknown about Babesia and very little of importance is known about Dactylosoma . This genus is known from Anura all over the world, and seems usually to occur in frogs and toads, in which the species is usually thought to be D. Ranarum. Other species have been occasionally reported from other amphibia and even from fish. Nothing at all is known of its transmission or life cycle. Its occurrence in frogs in very widely separated areas may have the same significance which Metcalf many years ago attached to the similar occurrence of the opalinids: it may be evidence for the existence in remote times of land bridges connecting land masses now remote from one another.