178 PROCEEDINGS OF THE AMEllICAN ACADEMY. 



American species. It was at Professor Thaxter's suggestion that the 

 present study of the cytology of certain species of these two genera 

 was taken up, in the hope of adding to our somewhat imperfect 

 knowledge of this, and especially, of ascertaining the relation of the 

 conditions involved in the formation of the resting-spores to the 

 conditions in other Phycomycetes. 



The first mention of the nucleus of Empusa is found in a paper by 

 Maupas, published in 1879. By staining with picrocarmine, he was 

 able to differentiate the nuclei, which, if seen by earlier observers, had 

 been considered to be vacuoles, and to show that the hyphae of Empusa 

 contain a large number of " petits nuclei, d'un diam^tre d'environ 

 4 microns." The next paper was that of Vuillemin ('87), who worked 

 with material of Entomoj)hthora gleospora, which was stained in haema- 

 toxylin but was not sectioned ; he describes the relatively large nuclei 

 (10 microns in diameter) regularly spaced in the hyphae, one nucleus 

 migrating without division into each conidium. Vuillemin made out 

 the presence of chromatin contents in the nucleus, but found no nucle- 

 olus. In 1899 appeared a preliminary note, soon followed by the 

 complete paper, by Cavara, describing the conditions in the hyphae and 

 conidia of Empusa Muscae and Entomophthora Delpinlana, including 

 also an incomplete account of the azygospores of the latter, Cavara's 

 paper was marked by an important technical advance, inasmuch as he 

 used microtome-sections with the most favorable stains. The follow- 

 ing year Vuillemin (-.00) published another paper on Entomophthora 

 gleospora, describing the behavior of the nuclei in the formation of the 

 azygospores, and including a theoretical discussion of certain points 

 concerning the relationships of the genera of the Entomophthoraceae. 

 These last two papers will be discussed in some detail in connection 

 with the results here presented on the cytological processes in several 

 species of Empusa and Entomophthora. 



Material and Methods 



In his "Monograph of the Entomophthoreae of the U. S." Thaxter 

 ('88) combined the species usually separated into Empusa and Ento- 

 mophthora in one genus under the name Empusa, considering that 

 the simple or divided character of the conidiophores, and the presence 

 or absence of rhizoids were features too inconstant to allow the separa- 

 tion of the species into two genera. Since, however, he has not been 

 followed in this procedure by other writers, and since, further, Cavara 

 (99'') has pointed out the importance of the fact that in the species 

 put in Empusa the conidia are typically multi- nucleate, while in those 



