RIDDLE. — ON THE CYTOLOGY OF THE ENTOMOPIITIIORACEAE. 187 



on material on the Spilosoma larvae ; but these have been confirmed in 

 every particular by material from the larvae of Hyphantria, 



Nucleus. 



The nuclei of Empusa are smaller (average diameter 4 microns), 

 more numerous in each hyphal body than in Entomophthora, and 

 show no regularity of spacing (Figure 23). The smaller size of the 

 nucleus makes it a less favorable object for study ; so far as has been 

 observed, however, the structure of the nucleus of Empusa agrees 

 perfectly with that of Entomophthora. Although caterpillars killed 

 by E. GrylU were fixed at various hours of the day and night, in 

 various conditions of moisture, and at longer and shorter periods after 

 death, no nuclear-divisions were seen in any case. It is therefore 

 impossible to state whether or not the details of this process also agree 

 with those in Entomophthora, as we should expect from the close 

 relationship of the two genera. 



Conidia. 



The general process of the formation of the conidia in Empusa 

 (Figures 2-4 and 2o) is similar to that already described for Ento- 

 mophthora. There are a few differences, however, the most important 

 of which is the fact that the conidia of Empusa are multi-nucleate 

 structures, and the conidiophores are unbranched. 



Some time before the death of the host the hyphae break up into 

 hyphal bodies in the usual manner ; and, at the time of death, each 

 hyphal body sends up a conidiophore. In this case, however, the 

 conidiophores and consequently the conidia are much larger than in 

 Entomophthora, conditions correlated with the absence of branching 

 in the conidiophore, and with the large amount of nuclear substance 

 in the multi-nucleate conidium. The nuclei in the conidiophore are 

 very numerous, and show no evidence of regular spacing (Figure 24). 

 There is the usual accumulation of dense cytoplasm in the tip of the 

 conidiophore as it swells to form the conidium. It will be recalled 

 that in Entomophthora a single nucleus passes into the young conid- 

 ium at this time. In the case of Empusa, a large number of nuclei 

 (about twelve to fifteen) pass in and the conidium is cut off. No nu- 

 clear-division takes place during this process of conidium-formation. 



After the discharge of the conidium, the nuclei left in the conidio- 

 phore degenerate, certain stages of this degeneration presenting a 

 misleading resemblance to the prophase of nuclear-division. The 

 nuclei can, however, be followed through all the stages of the process, 

 ending as vacuoles containing a few oil-like globules. 



