of the Fishery Board for Scotland. 



125 



drift-net from 14 to 16 hours previously. None lived more than two days 

 after arrival. They had usually lost a considerable number of scales. The 

 water in the barrel on March 5 was, on arrival at the Laboratory, 4*2° C. 



Experiments on the Pelagic Eggs of the Haddock (Gadus wglefinus) 

 and of the Plaice (Pleuronectes platessa). 



The haddock and plaice eggs were spawned naturally at the Laboratory. 

 The eggs of both species were collected on April 22. On the following 

 day they were put into a small wooden box which had a sieve bottom. This 

 box was placed in a metal egg-box (see p. 102), and the latter was jacketted 

 with ice. A small trickle of water flowed into the wooden box. On each 

 occasion when the temperature was taken the water was gently stirred with 

 the thermometer. 



On May 3 the eggs were floating, and on May 11 the eggs of both 

 species were seen to tend to stick to one another, more especially in the case 

 of the eggs of the haddock. The eggs of the plaice were at a stage near the 

 closure of the blastopore. 



On May 21 two plaice fry were obtained, and on May 24 several dead 

 fry of plaice and haddock were observed. The larva? were in both species 

 quite characteristic. One haddock egg had a fully-developed embryo in 

 which the heart was beating slowly. Some plaice eggs were floating, but no 

 haddock eggs. Some of the eggs of the latter were lying on the bottom dead. 



On each of the dates, May 28, 29, and June 1, some live plaiee 

 larvae were taken from the box. 



June 2. — Twenty-eight live plaice fry were removed. Three live plaice 

 eggs were seen. Two plaice fry were found on June 3, and the same 

 number on June 5. On June 6 the box was emptied. No live haddock 

 eggs were found. One dead haddock larva was noticed. One plaice larva, 

 and a live plaice egg hatching, were the sole survivors. 



The plaice eggs had hatched after an incubation period of 27 to 43 days. 

 An egg of the haddock was observed alive and unhatched after 30 days. 



The temperature of the water during the experiments is given in the table 

 on p. 126. Some plaice eggs were incubated between layers of felt moistened 

 by (a) the uncooled water of the hatchery and (b) by cooled water. The layers 

 of felt were packed in the bottom of a metal cylinder in the case of (a) and 

 in a wooden box for (6). The water was free to escape from the felt. 



The experiment was started on April 29 with eggs collected on the 

 previous day. 



On May 20 the uncooled eggs were examined, i.e., 21 days after the 

 initiation. Some dead larvae and some dead unhatched eggs were found. 



The water supplied to the cooled ova was that which came from the 

 cooled experiment of the haddock and plaice eggs. The temperatures 

 would therefore be nearly those given in the table, p. 126. 



On May 22 the cooled eggs were examined. Three dead larvae were 

 found. One larva was hatching. Some live eggs ready to hatch were 

 present, and some dead unhatched eggs. The eggs were put into ordinary 

 water. Some floated ; others sank to the bottom. 



On May 28 several larvae had hatched : the remaining eggs were dead. 



The object of the above experiments was attained when the larvae 

 hatched. The conditions were not suitable for the fry surviving. 



Reibisch* maintained that the number of days in the period of incubation 

 multiplied by the average temperature was a constant in each species. The 

 number of degrees centigrade was reckoned from a temperature at which 



* " Ueber den Einfluss der Temperatur auf die Entwickelung von Fisch-Eiern. " 

 Wiss. Meeresuntersuc/i. Komm, Kid u. Helgoland. N.F. 6 Bd. Kiel Abtheil, 

 1902. P. 215. 

 I 



