102 OOMYCETES. 



nospora and the Saprolegniacefe'no protoplasm can be observed to pass through 

 the fertilising tube, so that in these instances parthenogenesis takes place ; 

 Saprolegnia tlmretii, etc., have generally even no antheridia, but nevertheless 

 form normal oospores. Fertilisation of the egg-cell by means of self-motile 

 spermatozoids is only found in Monoblepharis sphcerica. 



A. Asexual reproduction by conidia only. 



Family 1. Entomophthorales. 



The mycelium is richly branched. The family is a transitional 

 step to the conidia-bearing Zygomycetes, since the oospores of many 

 members of this family arise, and are formed, like zygospores. 



Order 1. Entomophthoraceae. Mycelium abundantly de- 

 veloped. This most frequently lives parasitically in living insects, 

 causing their death. The conidiophores forming the conidial- 

 layer project from the skin, and abstrict a proportionately large 

 conidium which is ejected with considerable force, and by this 

 means transferred to other insects. These become infected by 

 the entrance of the germ-tube into their bodies. The spherical, 

 brown resting-spores develope inside the bodies of insects and 

 germinate by emitting a germ-tube. 



GENERA : Empusa has a good many species which are parasitic on flies, 

 moths, grasshoppers, plant-lice. The conidia emit a germ-tube which pierces 

 the skin of the insect ; a number of secondary conidia are then produced inside 

 its body, by division or by gemmation similar to that taking place in yeast, each 

 of which grows and becomes a long unbranched hypha, and these eventually 

 fill up the body of the animal, causing distension and death. Each of these 

 hyphse projects through the skin, and abstricts a couidium, which is ejected 

 by a squirting contrivance. The best known species is E. muscle (Fig. 85), 

 which makes its appearance epidemically towards autumn on the common 

 house-fly, and shows itself by the dead flies which are found on the windows 

 and walls attached by their probosces, distended wings, and legs. They have 

 swollen abdomen, broad white belts of hyphje between the abdominal rings, and 

 are surrounded by a circle of whitish dust formed by the ejected conidia. 

 Entomophthora sends out, at definite places, from the mycelium hidden in the 

 insect's body, bundles of hyphas, which serve the purpose of holding fast the 

 dead insects, the ramifications attaching themselves to the substratum : the 

 conidiophores are branched, the conidia are ejected by the divisional walls be- 

 tween the hyphre and the conidia dividing into two layers, those which ter- 

 minate the hyphae suddenly expanding and throwing the conidia into the air. 

 E. radicans makes its appearance epidemically on caterpillars. 



B. Asexual reproduction by zoospores or conidia. 



Family 2. Chytridiales. 



In this family the mycelium is very sparsely developed or is 

 wanting. The entire plant consists principally or entirely of a 



