WITH NOTES ON OTHER SPECIES. 81 



spores press each other so closely that they become irregularly polygonal. Finally 

 they escape separately through circular perforations of the sporangial wall, just as the 

 spores of Aclilya escape from their cysts, and swarm in the usual second form. The 

 close compression of the spores within the sporangium leads to a complete fusion of 

 the encvstins: wall of each one with those of the others which it touches and with the 

 sporangial wall. This must be, at least, the morphological explanation of the struc- 

 ture, although the membrane separating two spores may probably arise as a single 

 one. After the escape of the spores, as above described, there is left in the sporan- 

 gium a network of the apparently single walls which separated them (Fig. 112). 

 Their escape, like that of an Achlya or Soiprole'jnia spore from its cyst, is a slow 

 operation. The time from the beginning to the completion of the escape of the pro- 

 toplasm of a single spore may be half an hour or even more, and several houfs may 

 be occupied in the complete emptying of the sporangium. The separate spores follow 

 no order in their escape, but several in all parts of the sporangium may be escaping 

 together (Fig. 16). 



After its emergence the roughly globular mass contracts and becomes more ellip- 

 tical, while cilia appear and slowly lengthen. At length, twenty or thirty minutes 

 after escaping, in case of the undetermined species studied (Fig. 16), only four or six. 

 minutes after in D. monosporus, according to Leitgeb ('69), the spore darts away. 



In Aplanes, according to De Bary ('83), both swarming stages are suppressed, 

 and the spores, encysted within the sporangium, produce their germ tubes, which 

 pierce its wall and so reach the water, and perhaps fresh nourishment. But it must 

 be observed that their loss of the power of locomotion greatly diminishes the prob- 

 ability of this result. This lessened value of the sporangia as organs of propagation 

 may explain in some measure the fact that they are rarely developed in this genus. 



In Saprolegnia and Achlya those spores which encyst within the sporangium 

 may escape and swarm in the second form, or they may germinate ia situ. It is 

 evident that the former condition corresponds to a sporangium of Thraustotheca with 

 a permanent wall, or to one of Dlctyuchus in which the spore cysts have remained 

 separate, while the latter is just that which is normal for Aplanes. Abnormal 

 sporangia of genera whose spores are normally diplanetic may therefore be desig-^ 

 nated as " dictyosporangia," or as " aplanosporangia," according to the degree of 

 abnormality shown. Species of Dictyuchus may bear aplanosporangia. 



After the emptying of the first sporangium formed from a filament, which may 

 be termed a primary sporangium, a second one is very commonly developed from the 

 same hypha, and after it often a tertiary one, and so on for a variable number of gen- 

 erations. The sporangia of the second and later generations arise by one of three 



