436 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



passes from tlie antlieridium into the oospore, and effects fecundation. 

 (Fig. V, p. 433.) 



Thus the oosporangium represents a female reproductive organ, and 

 the oospore takes the place of an egg or an embryo cell. The antheri- 

 dium represents a male organ, and its contents represent the essential 

 substance of spermatozoids or the fertilizing matter of a pollen tube; 

 and, after fecundation, the oospores answer to impregnated ova or fer- 

 tilized seeds. 



The oosporangium may burst and give exit to the oospores, or it may 

 fall with them to the bottom. And, as a general rule, the oosiwres re- 

 main for a long time, sometimes several months, unchanged. Sooner or 

 later, however, they germinate, and this i^rocess may take place in vari- 

 ous ways: 



1. The contents of the oospore may divide directly into locomotive 

 zoospores, which are set free. 



2. The oospore may send out a hypha, the apical part of which be- 

 comes converted into a zoosporangium. 



3. The oospore may send out a hypha, and this coming into contact 

 with the body of a fly, or some such matter, may develoi)e into a myce- 

 lium in the ordinary way. 



The whole series of phenomena now described represents the fullest 

 set of changes known to occur in any one form of SaproJegnia. But, even 

 in the same form, the series may present notable variations. Thus, the 

 zoospores may germinate without passing into an active condition ,• or 

 they may germinate immediately after they assume the first quiescent 

 state. Again, in one and the same form, antheridia are sometimes 

 developed and sometimes absent. In some forms, indeed, anteridia 

 never make their appearance, and consequently fertilization does not 

 occur. Nevertheless, the unfertilized oospores germinate and produce 

 new Sajrrolcgnia', apparently just as well as if they were fertilized. 



The commonest species oi ISaprolegnia has received the name of JS.ferax, 

 and both Pringsheimand De Bary agree that several so-called species, 

 namely, ;S'. monoica, S. thvreti, and S. torulosa are merely more or less 

 l^ermanent varieties of S.ferax; that they are all, in fact, members of 

 the S. ferax grouj). 



It has been seen that the fungus which grows on diseased salmon is 

 unquestionably a species of the genus SaproJegnia ; and it is commonly 

 identified with S. ferax. But this identification has rested upon very 

 slender grounds. It is practically almost impossible to determine the 

 species of a l^aprolegnia until the characters of its oosporangia and of 

 its antheridia (if it have any) have been accurately made out. At pres- 

 ent, not only are we without any sufficient account of these organs in 

 the salmon Saprolegnia, but it is certain that they are, at most seasons, 

 extremely rare. Mr. Stirling* speaks of having observed only four in 



*Mr. Stirling's valuable contributious to our knowledge of the salmon disease are 

 contained in the "Proceedings of the Royal Society of Edinburgh " for 1878 and 1879. 



