438 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [12] 



The saltness given in the above table relates to the quantity of salt 

 which would be contained in a solution of cooking salt of the specific 

 gravity found in the sea.* Our areometers, according to Behrens and 

 Jacobsenj generally give the quantity of salt somewhat too high. 



Presuming that these observations also apply to the open sea, we find 

 that cod eggs, which require about 1.8 per cent, for floating, were dur- 

 ing the last eleven years laid in water, which on an average was too fresh, 

 four times in February, six times in March, and seven times in April. 

 We also find that during the three months referred to the water was 

 three times per month so fresh that the eggs could not float at all. For 

 the plaice eggs, which only require 1.78 per cent, salt, the average con- 

 dition of the water was too fresh, five times in March, three times in 

 April, and ten times in May. The maximum saltness did not reach the 

 necessary height 3 times in March, three times in April and seven times 

 in May. In the open sea the conditions of saltness may be somewhat 

 more favorable ; but beyond the Island of Eiigen, in the eastern part 

 of the Baltic, the sea water will hardly ever possess the degree of salt- 

 ness necessary for floating the eggs near the surface, unless the eggs in 

 those waters have a different weight. 



It did not seem probable that the saltness of the water would have 

 to be taken into consideration in observing the spermatozoa compos- 

 ing the spawn, as so far the observations had shown that, as a gen- 

 eral rule, J to IJ per cent, of cooking salt would sufSce to keep the 

 spermatozoa in healthy motion.f Nevertheless it seemed necessary to 

 investigate this matter. Strange to say it was found that the sperma- 

 tozoa of the cod and the plaice were influenced very strongly by the 

 degree of saltness of the water. Probably this whole subject is more 

 complicated than was supposed in the beginning. The condition of the 

 fish may have something to do with it, and the temperature may be of some 

 importJince. Observations made at a temperature of to 4°, however, 

 proved beyond doubt that mature spawn taken from the cod when not 

 diluted, did not show any motion, whilst, when placed in sea water 

 (taken from the aquarium) with a saltness of 1.9 per cent., it immedi- 

 ately showed very lively motions, lasting as long as one and a half hours. 

 I have certainly seen a spermatozoon (in the micropyle of an egg which 

 had probably been impregnated) in motion for that length of time. 

 When further diluted the general motion seems to decrease ; at 1.4 per 

 cent, and below the spermatozoa remain motionless for a period of one 

 to two hours, when there is again some motion, though less energetic 

 and less general. When the spawn is diluted by an admixture of light 

 sea water, there will always be a zone, within which the spermatozoa 

 will be in motion. In this case, however, the liquid of the spawn has 

 been suitably mixed with the water. This observation, however, should 



* See Meyer: " Unterauchungen uber die phygikalisohen VerhSltniase der Ostsee," p. 10. 



t Jahreabericht for 1871, p. 53. 



;See Hensen : " riiysiologie der Zeugiing"; Leipzig, 1881, p. 95. 



