112 TKANSACTIOXS AND PEOCEEDINGS OF THE [Sess.lxii. 



the constriction: the older portion may ultimately lengthen 

 to 260^, while the apical portion may give rise to another 

 constriction just behind its apex, and thus three super- 

 posed zoosporangia are formed. I have found two 

 commonly, three rarely, superposed. At the constriction 

 separating adjoining zoosporangia the passage becomes so 

 narrow as to prevent the escape of zoospores from one 

 sporangium into the other. 



The zoospores (or zoogonidia) do not escape from the 

 zoosporangia, but germinate inside the zoosporangia before 

 escaping ; the germinated zoospores are mostly spherical, 

 and average 13/i in diameter. 



I have not observed the sexual stage in any of the 

 material examined. Apodya lactcf.i, Cornu, is a saprophyte 

 throughout its whole life, and thus differs from Saprolegnia 

 ferox, which represents the most closely related genus in 

 the same order, Saprolcgniaccoi. Saprolegnia ferox, the 

 cause of salmon disease, is normally a saprophyte, living on 

 dead tish, etc., but it is also a facultative parasite, and lives 

 on the tissues of the living fish. 



The food of Apodga is organic matter, both nitrogenous 

 and carbonaceous ; the fungus, in common with all the 

 riiycoraycctcs, to which sub-class it belongs, is a rapid 

 grower, and also as rapid in its decay. 



Such a fungus, the existence of which depends on 

 pollution, absorbs some of the organic matter from the 

 water, but sooner or later it gives off decaying strands 

 which readily putrefy in passing down the stream. It has 

 been stated that the fungus Hoats on the surface, but I 

 have found that, whether living or dead, it always sinks in 

 still water. 



In conclusion, the action of Apodya is threefold : — It 

 removes oxygen from, and gives ofif carbon dioxide to, the 

 water, during its own life ; it takes the place of green 

 plants which act beneficially by removing carbon dioxide 

 from, and returning oxygen to, the water ; it removes 

 temporarily some of the organic polluting matter, and 

 returns it to the water afterwards in a putrescent condition 

 during the decay of its cast-off strands. 



The photomicrographs have been taken from specimens 

 mounted permanently in osinic acid, and for the careful 



