ZYGOMYCETES 



119 



of the sporangium divides about three times, forming eight thin-walled 

 sporangiospores, which rupture the sporangial membrane and are liber- 

 ated. If they are retained for a long time in the intestines of the frog, 

 they may multiply further by ordinary cell division, not by sprouting. 

 When they are excreted they develop the normal mycelium. In artificial 

 cultures, this process may be followed under extremely favorable condi- 

 tions, but ordinarily the sporangia germinate with one or more germ 

 tubes which soon end in a small secondary sporangium. The sporangia 

 also serve biologically as hypnospores, remaining alive for at least 9 

 months under laboratory conditions. Their ability to germinate either by 

 sporangiospores or by hyphae is reminiscent of conditions in Pythium 

 debaryanum of the Oomycetes. 



On the excrement, with failing nourishment, the mycelium begins to 

 form zygospores. Two neighboring cells, or two daughter cells of one 

 mother cell, put forth directly at their septa (in B. myophilus) one each 



Fig. 71. — Basidiobolus ranarum. Development of zygospores. 1. Nuclei resting in 

 the beaks with a pore already formed between the latter. 2. Completed plasmogamy. 

 3. Mature zygospores. (X 990; after Fairchild, 1897.) 



above and below, rostrate processes which approach and develop approxi- 

 mately to one-half the cross section of the sporiferous hyphae (Fig. 71, 1). 

 Both nuclei migrate into the beak and divide. Each daughter nucleus, 

 cut off at the tip by a more or less marked septum, degenerates. Both 

 other nuclei migrate basipetally. Meanwhile a pore is formed at the 

 base of the beak; the nucleus of one cell migrates into the other cell, 

 which has swollen in the meantime, and there lies beside the other nucleus 

 (Fig. 71, 2). Under certain conditions, yet insufficiently known, both 

 nuclei of the young zygospore may again divide amitotically, producing 

 four nuclei, of which two degenerate while the other two fuse. 



The young zygote withdraws considerable cytoplasm into itself, 

 swells much and surrounds itself with a thin membrane on whose inner 

 side is laid down a thick endospore of several layers (Fig. 71, 3). Gener- 

 ally caryogamy occurs only after two weeks; it may be hastened, however, 

 by desiccation and may then occur after three days; conversely it may be 

 retarded by favorable nourishment. After a rest period, the zygote may 



