446 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [20] 



liters — has to be examiued ; aud small crabs, diatoms, and medusae often 

 prove great hindrances. The eggs will cling so firm to the jelly-like 

 mass of the medusae, as soon as the water has been removed, that it be- 

 comes exceedingly hard to find them and separate them from the object 

 to which they adhere. The Sarsia, which became a special source of 

 annoyance, do not make their appearance in the Baltic in any consider- 

 able numbers till the end of the egg-period ; and they have finally to be 

 removed by means of a sieve in the wide openings. The diatoms which 

 often are found in quantities a hundred and thousand times as great as 

 that of the eggs, prove a serious hindrance. They and the entomostra- 

 cans — which are not near as annoying — can quickly be removed by means 

 of the following apparatus : To a metal tube having a diameter of 8 cen- 

 timeters little feet are attached, measuring from 3 to 4 millimeters in 

 length, so that it can be placed vertically on a glass plate. In this metal 

 tube another tube fits, which is partly arranged as a screw, so that ac- 

 cording to the necessity of the case, it may rise from 1 to 4 millimeters 

 above the glass plate on which it rests. Into this tubular vessel the 

 water containing the eggs is poured. The water immediately flows off 

 through the slit below, whilst the eggs aud all other larger objects re- 

 main on the glass plate. For the first idea of this exceedingly practical 

 apparatus — which I have only described above as to its leading i^rinci- 

 ples (in the improved edition it has only one foot) — I am obliged to 

 Count Spee, assistant at the physiological institute, to whom I hereby 

 also express my best thanks for his cheerful assistance during my excur- 

 sions. The tounting may be done conveniently after the tube has been 

 removed from the glass, by placing over the eggs a thin sheet of mica, 

 on which squares are marked. Unfortunately I did not have the o^jpor- 

 tunity of gathering observations in this respect. 



It need hardly be mentioned that the discovery of floating eggs an- 

 nounces to the scientific investigator the presence of the kind of fish 

 with which these eggs originate, and that, by following them against 

 the current, the spawning places must ultimately be reached, and that 

 the distribution of the eggs will indicate the direction of the currents. 



I shall now endeavor to explain the view that it is possible to obtain 

 an approximately correct estimate as to the quantity of the eggs. In 

 the first place a distinction must be made between the eggs which float 

 and those which do not float; for, as regards the latter, it seems utterly 

 imi)ossible to get at even an approximately correct estimate, and as re- 

 gards the floating eggs, it should be borne in mind that, if sufficient 

 time is allowed, they will gradually spread evenly throughout the sea 

 which is before them. I must confess that I have considered this fact 

 as self-evident, and have, therefore, neglected to gather experimental 

 data in this direction. I can therefore merely state that, (1) eggs which 

 were thrown into the sea for the purpose of impregnation did not remain 

 close together, but were scattered in a few minutes; (2) the result of my 

 observations given above (observations made at an interval of six days) 



