BULLETIN OF THE UNITED STATES FISH COMMISSION. 435 



tilameuts grow out and represent the primitive hyplifc of a new Sa^n'o- 

 legnia. (Fig. IV, p. 433.) 



If tlie spore has attached itself to some body which is incapable of 

 affording it nourishment, it may not germinate at all, or if it germinates 

 it speedily dies. But if it falls upon an appropriate soil, such, for ex- 

 ample, as the body of another dead fly, the spore sends a prolongation 

 inwards which perforates the tough chitinous cuticle of the fly, and gives 

 rise to a system of root-hyphae in its interior; while, simultaneously, it 

 grows outwards into a similarly ramifying stem-hypha, the branches of 

 which soon enlarge into zoosporangia and give rise to zoospores, as 

 before. 



The growth and development of the Saprolegnia take place with ex- 

 traordinary rapidity. In 3G hours from the first infection of the body 

 of a dead fly with the Saprolegnia spores, it may be covered with a thick 

 coat of stem-hyphte a fifth of an inch long; and in the course of the 

 second or third day a thousand of these may have developed and emii- 

 tied their sporangia, thus setting free some 20,000 zoospores, every one 

 of wliich is competent to set up the same process in a new fly-corpse. 

 As all this production takes place at the expense of the tissues of the 

 fly, the supply of imlritive material gradually diminishes. At about 

 the fourth daj^, or perhaijs not till later, new forms of sporangia, termed 

 "dictyosporaugia," (Fig. Ill, p. 433,) in which the spores encase them- 

 selves and often germinate while still within the sporangium, make 

 their apx>earance, and the ordinary zoosporangia diminish in number. 

 Xot unfrequently, about this time or subsequently, the hyphiie tend to 

 break up into short joints which are themselves capable of germination. 

 Finally, after the fifth or sixth day, a new kind of sporangium usually" 

 makes its appearance, which is termed an Oosporangium^ inasmuch as 

 the spores to which it gives rise are more like eggs or seeds than the 

 products of the zoosporangia or those of the dictyosporaugia. 



The summit of a hypha, or a short branch of a hypha, dilates into a 

 spheroidal sac, the cellulose wall of wliich becomes thickened, but pre- 

 sents here and there thin places, looking like clear circular dots or aper- 

 tures under the microscope. Protoplasm accumulates in the spheroidal 

 case thus formed, and either remains a single rounded mass, or divides 

 into a smaller or greater number of spheroids, each of which, much 

 larger than a single zoospore, is an Oospore. The oospore or oospores 

 thus formed eventually become invested by a thick cellulose coat. Be- 

 fore this hai)peus, in some forms of Saprolegnia, slender twig-like 

 branches are given off either from the stalk of the oosporangium or 

 from an adjacent hypha, and the terminal portion of one or more of 

 these twigs applies itself to the oosporangium. This terminal portion 

 becomes shut off" from the rest of the twig by a transverse septum, and 

 is an Anther id ium. The antheridium pierces the wall of the oosj^oran- 

 gium, divides into as many branchlets as there are oospores, and one 

 branchlet applies itself to each oospore. In all probability something 



