Proceedings of the American Academy of Arts and Sciences. VOL. XLII. No. 10. AUGUST, 1906. CONTRIBUTIONS FROM THE CRYPTOGAMIC LABORATORY OF HARVARD UNIVERSITY. - LXIII. ON THE CYTOLOGY OF THE ENTOMOPHTHORACEAE. BY LINCOLN WARE RIDDLE. WITH THREE PLATES. CONTRIBUTIONS FROM THE CRYPTOGAMIC LABORATORY OF HARVARD UNIVERSITY. — LXIII. ON THE CYTOLOGY OF THE ENTOMOPHTHORACEAE. BY LINCOLN Ware Riddle. Presented by W. G. Farlow, May 9, 1906. Received May 14, 1906. INTRODUCTION. THE Entomophthoraceae constitute a small, and, in some ways, peculiar family of Phycomycetes, including, according to Schroeter's arrangement in Engler & Prantl, seven genera. Of these seven genera, we have more or less knowledge of the nuclear conditions in four. In Conidiobolus (Brefeld, '84) we know only that the hyphae are nonseptate in the early stages, but in the older stages break up into short sections (hyphal bodies) which are multi-nucleate. Basidiobolus (Eidam, '87) is perhaps the best known of the genera from a cytological point of view, chiefly on account of the work of Fairchild ('97), although the papers of Raciborski ('96), Lowenthal (:03), and Woycicki (:04) are also to be mentioned. The hyphae are here septate, dividing the fungus into cells, which are typically uni-nucleate; the conidia also possess single nuclei, derived directly without division from the parentcells. The zygospore is formed by the fusion of the nuclei of two adjacent cells, this process being preceded, however, by the production of two beaks on the fusing cells, with a simultaneous division of the two gamete-nuclei so that a daughter-nucleus is cut off in each beak, while the other two daughter-nuclei enter the young zygospore and sooner or later fuse. Raciborski ('96") and Fairchild ('97) have both described the division of the nucleus of Basidiobolus by a mitotic method. The two remaining genera, upon which a certain amount of cytological work has been done, are Empusa and Entomophthora, all the species of which are parasitic on the larvae, pupae, or imagines of various insects, and resemble one another in their general life-history. For the general morphology of these genera reference may be made to the account given by Thaxter ('88) in his monograph of the North VOL. XLII.-12 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 diamètre d'environ * 4 microns." The next paper was that of Vuillemin ('87), who worked with material of Entomophthora gleospora, which was stained in haematoxylin 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 nucleolus. 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 Delpiniana, 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 following 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 Entomophthora 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 separation 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 |