188 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



III. — CAUSE OF THE NON-DEVELOPMENT OF FUNDUS ON THE EGOS 

 HATCHED IN THE MCDONALD JAR. 



The development of fungus on shad eggs, as far as we are able to judge, 

 has always been due to the conditions under which they were placed. 

 When any imperfection existed in the current of water flowing through 

 the cones, the eggs which would collect on some spot on the bottom 

 screen which had been partially choked up with sediment, caused both 

 dead and live eggs to collect in a mass over such places. The fungus, 

 on account of its very rapid development, when once started amongst 

 such lots of eggs, would soon mat them together in large masses, which 

 had to be removed with the small " skim net." The absence of any cur- 

 rent amongst masses of ova seems to be the one favoring condition un- 

 der which the egg-fungus grows most advantageously. The mycelium, 

 once established on the membranes of a lot of eggs, soon attacks those 

 which some movement may bring into contiguity with those already in- 

 fested. The plant possesses all the features of a parasite converting 

 the material of the egg into its own substance. Its reproductive activi- 

 ties are also developed very early, and its germs are produced in vast 

 numbers, which are very minute motile bodies which escape from their 

 receptacles on the parent plant to pollute the surrounding water. It is 

 easy on this account to understand that any apparatus from which it is 

 impossible to effectually remove dead eggs, and in which there is an 

 imperfect circulation of water amongst the latter, would favor the de- 

 velopment of fungus and the destruction of many ova. Formerly the 

 Bell and Mather cone was disposed, if not carefully watched, to favor the 

 development of fungus. Eecently thisobjectionablefeatureseemstohave 

 been overcome to a certain extent. No " cone " yet devised is, however, 

 as good as any one of three different forms of glass apparatus; the 

 Chase, the Clark, or the McDonald jar offer advantages over any form of 

 metal apparatus. These systems of glass-hatching vessels can be kept 

 so thoroughly free from dead eggs without a skim net, and the circula- 

 tion can be so perfectly regulated so as to keep every egg in continuous 

 movement, thus preventing any fungus spores from lodging on the eggs. 

 The continuous and gentle attrition of the ova in the glass jars effectu- 

 ally prevents any fungoid germs from adhering to the membranes of 

 the ova; the pest, which is in this way prevented from obtaining a foot- 

 hold, never causes any serious trouble. 



Another advantage offered by the glass jars is the ease and accuracy 

 with which the number of eggs may be estimated by graduating the 

 jar into inches or into intervals indicating the spaces occupied by sin- 

 gle thousands of eggs, or by measuring the height of the column of 

 eggs in the jar with a graduated rule indicating similar quantities. 

 This also enables the person in charge to estimate very closely the num- 

 ber of dead eggs which accumulate on the surface of the live ones in a 

 layer of nearly even thickness. This is impossible in the metal cones, 

 and the estimate of losses has hitherto been little better than guess- 



