The body never possesses an epimerite and is non-septate. Chiefly coelomic parasites of "worms," Holothurians and insects. The _Aseptata_ have not been so completely arranged in families as the _Septata_. Leger has distinguished two well-marked ones, but the remaining genera still want classifying more in detail. Fam. _Gonosporidae_, with _Gonospora_, _Diplodina_; and _Urosporidae_, with _Urosopora_, _Cystobia_, _Lithocystis_, _Ceratospora_; the genera _Monocystis_, _Diplocystis Lankesteria_ and _Zygocystis_ probably constitute another; _Pterospora_ and, again, _Syncystis_ are distinct; lastly, certain forms, e.g. _Zygosoma_, _Anchora_ (_Anchorina_), are incompletely known. There remains for mention the remarkable parasite, recently described by J. Nusbaum (24) under the appropriate name of _Schaudinnella henleae_, which inhabits the intestine of _Henlea leptodera_. Briefly enumerated, the principal features in the life-cycle are as follows. The young trophozoites (aseptate) are attached to the intestinal cells, but practically entirely extracellular. Association is very primitive in character and indiscriminate; it takes place indifferently between individuals which will give rise to gametes of the same or opposite sex. Often it is only temporary; at other times it is multiple, several adults becoming more or less enclosed in a gelatinous investment. Nevertheless, in no case does true encystment occur, the sex-cells being developed practically free. The female gametes are large and egg-like; the males, minute and sickle-like, but with no flagellum and apparently non-motile. While many of the zygotes ("amphionts") resulting from copulation pass out to the exterior, to infect a new host, others, possessing a more delicate investing-membrane, penetrate in between the intestinal cells, producing a further infection (auto-infection). Numerous sporozoites are formed in each zygote. It will be seen that _Schaudinnella_ is a practically unique form. While, on the one hand, it recalls the Gregarines in many ways, on the other hand it differs widely from them in several characteristic features, being primitive in some respects, but highly specialized in others, so that it cannot be properly included in the order. _Schaudinnella_ rather represents a primitive Ectosporan parasite, which has proceeded upon a line of its own, intermediate between the Gregarines and Coccidia.