1. The occurrence of Adelina cryptocerci in the host, Cryptocercus punctulatus, and its probable means of natural transmission are discussed.
2. Artificial infection experiments were carried out and furnished material for determination of succession of stages in the life cycle of the organism. The cycle is briefly as follows:
(a) Mature cysts are ingested by the hosts with tissues of infected roaches. Sporozoites enter the host's tissues by passing through the midgut wall.
(b) The first schizogony, in which merozoites are produced, ocurs in the fat-bodies between the sixteenth and twenty-fifth days after ingestion of cysts.
(c) In the second schizogonial generation two types of schizogony produce merozoites and gametoblasts, respectively, between the twenty-fifth and twenty-ninth days following infection. There is evidence that both male and female gametoblasts are formed from a single schizont.
(d) Male and female gametoblasts become associated during the growth period of the latter. When fully grown, they are surrounded by a membrane, the gametocyst. The male gametoblast undergoes 2 divisions, forming 4 microgametes, of which 1 fertilizes the macrogamete and the other 3 lie unused between the gametocyst and the first oocyst, which is formed shortly after fertilization. A second oocyst is formed before the first division of the synkaryon.
(e) By repeated divisions of the synkaryon a multinucleate sporont is formed. This divides into uninucleate sporoblasts. Each sporoblast divides once, forming a sporocyst containing 2 sporozoites. Mature cysts occurred in experimentally infected roaches from 40 days onwards.
3. The stages in the life cycle are described in detail.
4. Evidence for zygotic meiosis in Adelina cryptocerci is presented.
5. The effect of the parasite on the host is discussed.
This investigation has been made at the suggestion of Dr Harold Kirby, Jr., and under his direction and that of Dr C. A. Kofoid. I wish to express here my grateful appreciation to both for their interest and many valuable suggestions and criticisms.