A trophozoite (meront) of _N. apis_ becomes a single pansporoblast which gives rise to one sporoblast producing one spore, and this procedure is characteristic of the genus _Nosema_. In other genera the trophozoite may form more than one pansporoblast and each pansporoblast may form a variable number of spores in different cases. Various attempts at classification have been based on these characteristics. It must suffice here to note that in the cases where the trophozoite becomes one pansporoblast, the latter can produce four spores in the genus _Gurleya_, eight spores in _Thélohania_ and many spores in _Pleistophora_. In other cases, where the trophozoites give rise to many pansporoblasts, each of the latter may form many spores, as in the genus _Glugea_. A few pathogenic microsporidian parasites other than _N. apis_ may be mentioned. _N. bombycis_, causing pébrine in silkworms, may infect any or all the tissues of the host (fig. 99). The larvæ of the host, _i.e._, the “silkworms,” may become infected by eating food contaminated with spore-containing excrement of already infected silkworms. In cases of heavy infection the silkworm dies, but should the infection be less intense the larva becomes a pupa in which the parasite persists, so that the moth emerges from the cocoon already infected. Not only is the moth parasitized itself, but the Nosema reaches the generative organs of both sexes and penetrates the ovaries of the female, with the result that the ova are deposited infected. Such infected eggs are capable of developing, so that infection may be transmitted hereditarily as well as by the contaminative method. Infected eggs can be recognized by microscopic examination, as Pasteur showed, and thus preventive measures may be adopted. A microsporidian parasite is known to occur on the roots of the spinal and cranial nerves of _Lophius piscatorius_, the angler fish. This parasite is variously referred to the genera _Nosema_ and _Glugea_. _Thélohania contejeani_, parasitic in the muscles of crayfish, is believed by some to be the causal agent of recent epizoötics among them, though others believe the disease to be really due to a bacillus. It may be that the one organism aids in the entry of the other into the host. Order. *Actinomyxidia*, Stolč. A brief mention may be made of the Actinomyxidia (fig. 101), which were first described by Stolč in 1899 as parasites of Oligochætes. They have also been investigated by Mrazek, and a detailed study of certain species was made by Caullery and Mesnil (1905). The trophozoite is small and amœboid. The spores are large, and exhibit tri-radiate symmetry. Spore formation is complicated and sexual processes occur therein. Many amœbulæ are set free from each spore.