INSECT FUNGI 191 



tion occurs only when hyphae of the two kinds come into 

 contact (heterothallic forms). 



287. The Insect-fungi (Entomophthoraceae) are well 

 represented by the Fly-fungus (Entomophthora muscae), 

 which in the autumn is destructive to house-flies. It 

 consists of small tubular coenocytes which grow in the 

 moist tissues of the fly, and at last pierce the 

 skin, producing minute terminal spores, which 

 give the fly a powdery appearance. These 

 spores (called, also, conidia) may be seen as a 

 whitish halo surrounding the spot to which the 

 fly (now dead) has attached itself. Round 

 and thick-walled resting spores (formed by 

 the union of gametes similar to those of Black 

 Molds) have been observed in some species, and may be 

 studied in the Grasshopper Fungus (Entomophthora 

 grylli), which destroys great numbers of grasshoppers 

 every autumn. 



The Sexual Organs of the Water Molds, Downy Mil- 

 dews, Black Molds, and Insect Fungi show a progressive 

 degeneration from the typical structure occurring in the 

 Green Felts. In the Water Molds there is a suppression 

 of the sperms, the antherid protoplasm being transferred 

 directly to the egg. This is continued with little change 

 throughout the Downy Mildews and White Rusts, which 

 being non-aquatic could scarcely make use of motile 

 sperms. The sexual organs of the Black Molds are 

 apparently of the same general type as those of Water 

 Molds and Downy Mildews, each being an end cell cut 

 off from a reproductive filament, but in Black Molds 

 these filaments show little differentiation. They unite 

 prematurely, before the oogone has developed an egg, 

 and before the other filament has developed its anther- 

 idial protoplasm. They are physically under-developed 



