ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 73§ 



fluids of marine animals and the sea- water. He has experimented on 

 the eggs and larvae of Teleosts and Elasmobranchs. 



The freezing-point of the contents of plaice-eggs is very different 

 from that of the sea-water in which they are fonnd floating, and the 

 osmotic pressure is only about two-fifths that of the latter. The freezing- 

 point of the contents of dog-fish eggs is about the same as that of the 

 sea-water. 



Immersion of dog-fish eggs in a fluid of less salinity than normal 

 sea-water, results in a gain in weight due to absorption. The contents 

 of the purse are therefore not independent of the external medium, and 

 a change in salinity of the latter brings about an alteration in the 

 salinity and osmotic pressure of the egg-contents. 



The osmotic pressure of the egg-contents in plaice and dog-fish re- 

 sembles very closely that of the blood of the adults. In the case of the 

 pelagic eggs of the plaice, death results in a disturbance of the conditions 

 under which the equilibrium existing between the egg-contents and the 

 sea-water is maintained, and an increase in the salinity of the egg- 

 contents accompanied by an increase in density takes place, with the 

 result that the eggs can no longer float. 



Retarding Development of Herring's Eggs.* — H. Chas. Williamson 

 has been able, by lowering the temperature of the water, to prolong the period 

 of embryonic development to fifty days. This is with a view to facilitating 

 importation to New Zealand. Further experiments in extending the 

 period have proved unsuccessful, and the author recommends that the 

 eggs should be put as soon as possible after spawning into running 

 water, or water kept in motion, and that effective mechanical aeration be 

 secured. 



Colouring of Trout.f — K. Wagner has made a study of the develop- 

 ment of the coloration in the young trout {Sahno fario). The original 

 pigment is the lipochrome of the yolk-sac. The first melanoblasts 

 appear, at a temperature of 7-10° C, some fourteen days before hatching. 

 In other Teleosteans that have been described the time noted is about 

 the time of hatching. 



The first melanoblasts separate off from the uppermost portion of 

 the muscle-segments. There is progressive pigmentation in situ and 

 also active migration. The epidermis remains quite unpigmented. 



The bands of colour differ from other parts not in having more 

 chromatophores, but in having them in different state of expansion. 

 They function independently of the rest of the body. 



The first orange-red colouring is found associated with ramified cells 

 of the connective-tissue. These cells appear about a week later than the 

 melanoblasts. The plasma of the orange-red cells is filled with an oil- 

 like mass, in which a variable quantity of lipochrome has been dissolved. 

 The cells form in their interior the subsequently extra-cellular lipochrome 

 drops, which unite in the red spots of the older trout. There are also 

 carmine-red drops and an iridescent granula. 



* Fishery Board Scotland, 28th Rep. (1911) pp. 16-23 (1 pi.). 

 t Internal Rev. Hydrohiol., iv. (1911) pp. 1-33 (1 pi.). 



