iQig] WESTON— DICTYUCHUS 291 



After the zoospores (figs. 8, 9) have emerged, their general struc- 

 ture and the disposition of the cilia are seen to be very similar to 

 the "secondary" laterally biciliate type in other genera of the 

 family, although these zoospores are longer and more tapering 

 than those of Achlya and Thraustotheca, while more flattened than 

 those of Saprolegnia. On an average the zoospores of our form 

 are about 13 /z long and 10 ix wide. After an active period of 

 variable duration they come to rest, lose their ciHa, and encyst, 

 forming spherical, coarsely granular spores which, to avoid con- 

 fusion, will be called " cystospores " (fig. 10). After a time these 

 may germinate by sending out hyphae in a perfectly normal 

 manner (figs. 16, 17). 



When the sporangiospores give rise not to zoospores but to 

 hyphae of germination, the latter push through the enveloping 

 sporangium wall and grow out into the water (fig. 18) in a manner 

 quite similar to that which is said to be. characteristic of Aplanes. 

 It is to be noted, however, that in Dictytichus, as well as in other 

 genera in which it occurs as an abnormal method of development, 

 such germination only takes place in. the presence of nutrient 

 substances, or of such non-nutrient materials as prevent zoospore 

 emergence. 



It is clear that the cycle of non-sexual spore formation just 

 described agrees entirely with the usual accounts. In the form 

 under discussion, however, an additional zoospore emergence may 

 take place. This phenomenon was repeatedly observed under the 

 following conditions: A piece of agar covered with mycehum, 

 Avhen transferred from a stock culture to dilute beef extract, 

 rapidly grows to a small compact tuft of h>phae. If this tuft, 

 after a thorough washing to remove the adhering nutriment, is 

 placed in a hanging drop for study, sporangium formation rapidly 

 takes place, and from the sporangiospores large numbers of zoo- 

 spores emerge and swim about. Finally they come to rest and 

 encyst for the most part along the edge of the drop. After a 

 time some of the encysted spores so situated germinate by hyphae. 

 Many, however, emit zoospores, with the result that all along the 

 ■edge of the drop may be seen empty cystospores and zoospores 



