186 PROCEEDINGS OF THE AMERICAN ACADEMY. 



inner side, this clearer zone is marked off by a densely granular region. 

 The conditions at this period suggest strongly the periplasm found in 

 so many Phycomycetes. This appearance, however, may be accidental 

 and without special significance. From a study of such stages as are 

 illustrated by Figure 15, it is evident that the granular cytoplasm is 

 being gradually transformed into the clear material of the mature endo- 

 spore (Figure 16). The endospore in Entomophthora thus appears to 

 be formed, not as a secretion of the outer plasma-membrane, but by 

 a direct transformation of the outer zone of cytoplasm, this transforma- 

 tion evidently involving more than the plasma-membrane itself, and 

 possibly representing a primitive type of periplasm. 



After this formation of the endospore, the zygote enters into a rest- 

 ing period which lasts until the following summer. Sections cut from 

 material fixed three months after formation show that no fusion of the 

 nuclei has taken place up to that time (Figure 16). Whether or not 

 fusion of the nuclei in pairs takes place at the time of germination, as 

 we might expect, it has been impossible to determine, owing to the 

 difficulty of germinating the zygospores under artificial conditions. 

 That the process of zygospore formation thus given for E. Americana 

 is confirmed in full by E. echhiospora may be seen by comparing Fig- 

 ures 11 to 16 with Figures 20 to 22. 



It will be seen from the foregoing description that the processes con- 

 nected with the formation of the sexual resting- spores in Entomoph- 

 thora are closely comparable with the corresponding processes in the 

 Mucorales, in so far as they have been made known by the work of 

 Gruber (:0l) on Sporodinia. Entomophthora has, in common with 

 Sporodinia, coenogametes (multi-nucleate sexual cells) which are of a 

 simple type, inasmuch as there is no differentiation of the contents 

 and all of the nuclei function as gamete-nuclei. 



Empusa. 



Material of E. Gryll'i on two different hosts furnished the preparations 

 upon which was based the study of this genus. Under E. Griilli, Now., 

 Thaxter ('88) included as a synonym E. AuUcae, Reichhardt (in Bail, 

 '69) first described on Euprepia aulka, but also occurring on other 

 hosts, and especially in the United States, on the larvae of Spilosoma. 

 Several authors (Cohn, '75 ; Schroter, '86 ; Lindau, '97) have kept this 

 as a distinct species. The writer, in the course of the present study, has 

 seen no such differences as should be considered of specific rank, and 

 therefore prefers to follow Thaxter and consider both of the above forms 

 as true Empusa GrijlU, Nowakowski. The results here given are based 



