122 Fart III. — Twenty-seventh Annual Report 



Where the spawn is on glass plates it is probable that a mechanical 

 system of aeration would be most suitable. As the experiments were con- 

 ducted, none of the water was used over again. If it were possible to use 

 the cooled water a second time it would simplify the cooling arrangements, 

 and it would be possible to give a stronger current. This would require a 

 special small pump. 



It is probable that an average temperature of 2° C. (35-5° F.) would be 

 sufficient to prolong the incubation-period to 50 days. 



Crystals Inside the Eygs. — Crystals (figs. 2, 6, 26, 49) were commonly 

 observed in the cooled eggs and also in some uncooled eggs. It is possible 

 that these are excretory products formed during the development of the 

 embryo. The low temperature or the deficient water circulation may not 

 have been helpful to the removal of the product, which had accumulated 

 both inside and outside of the zona. The water circulation probably plays 

 two rdles — the supply of oxygen and the removal of excretory products. 



Tlie Fertilization of the Egg of the Herring. 



Brook* agreed with the conclusion of Kupflfer that the formation of the 

 perivitelline space in the egg only took place after fertilization. The 

 envelope of the egg, when pressed out of a ripe female, is thick and some- 

 times bossed. When the perivitelline space has appeared the envelope is 

 thinner and smoother. 



Brook found that the ova retain their vitality 40 to 48 hours after the 

 female is dead, but that the spermatozoa do not retain their vitality for more 

 than three houi'S after the death of the fish. 



A male herring was dissected on February 20, 1908, 24 hours after 

 death. A piece of the ripe milt was put into sea-water. At first the sperms 

 were almost motionless. Then they began to oscillate, and finally a few of 

 them moved vigorously. They seemed to be united in groups ; the tails 

 were not made out. Their oscillations, although very marked, were not of 

 the same nature as that of the live sperms of plaice, for example. The 

 sperms, although apparently alive, were dead. 



The Herring Fry. 



The larval herring (fig. 55) is very translucent. The only pigment visible 

 by means of the dissecting microscope is a row of 24 black corpuscles 

 extending along the ventral edge of the muscle segments from the hind edge 

 of the yolk-sac to the anus. There seems to be associated with them a little 

 red pigment. A few corpuscles are visible at the end of the tail. The eye, 

 which is silvery (reddish when seen from certain angles), has a black pupil 

 and a black under-edge. The mouth is large, and is fixed wide-open. It is 

 somewhat quadrangular in shape (m, fig. 54), and is underhung. The gill- 

 ^.rches can be faintly m^ade out. The little fish wriggles about after the 

 manner of an eel, and in general appearance recalls the larva hatched from 

 the Mursenoid eggs of Raffaele.t 



A difference in size was noticed among the fry from one of the lots of 

 cooled spawn. The larger seemed to have the smaller yolk-sac. Meyer 

 drew attention to a similar condition at Kiel. The larvae hatched out in 

 September (YL, p. 120), were rather smaller than a sample obtained from 

 eggs hatched in April (V., ih.). A sample of herring fry obtained 24 miles 



t Brook — "On the Development of the Herring." Part II., Plates I. and II., 

 Fourth Report of the Fishery Board for Scotland for the year 1885. Edinburgh, 

 1886, p. 31. 



* Raffaele — "Uova gallegianti del Golfo di Napoli," Mittheil. Zool. Station 

 Neapel. Bd. 8, 1888; and M'Intosh and Masterman, "The Life Histories of the 

 British Marine Food-Fishes." London, 1897. Plate XX. , fig. 6. 



