4 A. E. HEFFORD. 



and dab, as well as approximately the same spawning period, while 

 the same can be said regarding Capros aper as compared with the 

 gurnards. 



In the course of my laboratory observations, a point which has 

 struck me as interesting and worthy of further definite inquiry, is the 

 relative vitality of the eggs of various species, as indicated by the 

 extent to which they are affected by the conditions under which they 

 are kept while under observation, in the course of their development 

 in the laboratory. On several occasions I have kept ova of different 

 species in the same vessel of sea-water in order to watch the process 

 of development and examine the hatched-out larvae. In sucli cases it 

 frequently happened that one species would do well and produce 

 healthy and vigorous larvae, while another would fare badly, and, if the 

 embyro survived so long as to hatch out, the resulting larva would l)e 

 more or less moribund from the outset and frequently crooked in 

 shape. Notable among those whose vitality in the laboratory was 

 considerable were the eggs and larvae of Motella mustela, Callionymus 

 hjra, and Ctenolabrus TKpcstris, while those which most often appeared 

 to be adversely affected were Gadus, Trigla, and especially the rare 

 forms Raniccj)S raniniis and Serraniis cahrilla. It is to be expected that 

 natural selection has effected that inshore — and sometimes even 

 estuarine — forms like Motella mustela and Ctenolabrus rupcstris should 

 produce eggs which are capable of a wider range of environmental 

 change (e.g. of temperature, to take the most obvious factor which 

 operated in the cases under discussion) than those species which spawn 

 in deeper water, where the surrounding conditions are of a more 

 uniform character. In the case of Sej-ranns eahrilla it is not sur- 

 prising that ova produced in this neighbourhood, which must be at 

 the extreme limit of the natural spawning area of this species, 

 should be of less than average health. The laboratory temperature 

 falls below that of the sea at times in winter, and in summer is gener- 

 ally above it. In the hot weather my vessels containing eggs were 

 put to stand in running aquarium water for the sake of coolness. 

 The same should be done if frost is to be feared in winter. I kept my 

 eggs in sea-water obtained from well outside the Sound, or in aquarium 

 water which had been treated with animal charcoal and then filtered 

 through a " Berkefeld " filter.* 



* See Allen and Nelson, "On the Artificial Culture of Marine Plankton Organisms," 

 Joura. M.B.A., Vol. VIII, No. 5, p. 432. 



