188 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The centre of the mature conidium is pretty constantly occupied by 

 a single, large, well-defined vacuole around which the numerous, much 

 condensed nuclei are most often clustered (Figure 25). 



The conidia of Empusa Grylli are, then, multi-nucleate structures 

 and corroborate the statement of Cavara ('99*), based on his examina- 

 tion of E. Muscae, that a multinucleate conidium is characteristic of 

 the genus Empusa, while, as the same author shows in Entomopkthora 

 Delpiniana^ and as has been shown above for a number of other species 

 of the genus, Entomophthora has constantly a uni-nucleate conidium. 

 The conidia of Empusa are also to be compared to those of Albugo and 

 other genera of the Peronosporales, where, in all forms which have been 

 examined (Ruhland, :03), the conidia are multi-nucleate. But the 

 absence of a nuclear-division preceding conidium-formation in Empusa 

 is in marked contrast to that of Albugo, a difference to be explained 

 by the fact that, while in Albugo a series of conidia are formed, in 

 Empusa but a single conidium is formed from each conidiophore. 



, Azygospores. 



Just as the hj^hal bodies and conidia of Empusa are multi-nucleate 

 structures, so also we find multi-nucleate conditions in the azygo- 

 spores. This multi-nucleate condition appears from the first formation 

 stages, and these nuclei undergo neither divisions nor fusions. As 

 these observations are not in accord with those of previous workers on 

 the azygospores of Entomophthora, namely Cavara ('99) on E. Del- 

 pmiana and of Vuillemin (:00) on E. gleospora, it will be well to 

 examine their results before describing the development of the azygo- 

 spores in Empusa. 



In Entomophthora Delpiniaria, a species in which the hyphae do 

 not break up into hyphal bodies, Cavara observed two sorts of struc- 

 tures which he called azygospores. First, a thick-walled, intercalary 

 organ with granulated cytoplasm which shows clear reticulations, the 

 joints of the meshes being occupied by " chromophilous granules " ; 

 this organ contains no definite morphological nucleus, but Cavara 

 regards the " chromophilous granules " as a diffused nucleus. Such 

 an intercalary organ appears not to have been seen by any other 

 workers. Certainly in the present study no structures have been seen 

 resembling Cavara's description, so that an interpretation of these 

 curious conditions is here out of the question. Secondly, and more 

 commonly, Cavara finds an organ of acrogenous formation ; a hypha 

 swells at the end into an ampulla ; into this ampulla passes a single 

 nucleus ; a cross-wall is then formed cutting off the spore, which is, 

 therefore, at this time, uni-nucleate ; this single nucleus divides to 



