The myxosporidia belong to the class sporozoa (Leuckart), a sub-division of the sub-kingdom protozoa. The sporozoa are unicellular parasitic organisms, obtaining their nourishment by the absorption of the liquids of their host. This class of parasites is particularly interesting to the pathologist at the present time, because of their supposed causative relation to carcinoma and other neoplasms. The classification of the sporozoa lately adopted by Braun is that of Mingazzini, who divides them into four groups:—1. Gregarinida (including coccidia). 2. Myxosporidia. 3. Sarcosporidia (including microsporidia). 4. Hæmosporidia. From this it will be seen that the myxosporidia form a separate group of the sporozoa, having been set aside in this manner because of certain characteristics peculiar to themselves; and in this grouping, the principal feature which distinguishes the myxosporidia from other sporozoa, is the presence of thread-like flagellæ in their spores.
The life history of most of the sporozoa is still