8 Fishery Board for Scotland. 



following quantities of" fry were obtained : — 39th daj', 120 (20 dead)* : 

 40th, 250 (20 dead); 41st, 191; 42nd, 335 (100 'dead); 43rd, 160 

 (10 dead) ; 44th, 187 (10 dead) ; 45th, 98 (4 dead) ; 46th, 67 (8 dead); 

 47th. 24 (2 dead); 48th, 27 (1 dead); 49th, 16 (5 dead): 50th. 14 

 (4 dead) ; 51st, 8 (3 dead) ; 52nd, 1 ; 53rd, 1 larva. 



After the 39th day the larvae seemed normal. They were shorter 

 on the whole than the average larva, and they had a comparatively 

 large amount of j'olk still remaining unabsorbed. The heads were 

 flexed. They wriggled about quite actively with eel-like movement. 

 On the 47th day two measured 7 and 8 mm. i-espectively. The head 

 was onh' slightly flexed. On the 50th da}^ 10 good fry showed still a 

 good quantity of yolk. The heads were slightl}^ flexed. 



The hatching of the ova began prematurely in consequence, I 

 consider, of the decay of the zona, caused by the diatoms attached to 

 it. The same cause led, in my opinion, to the death, through 

 suflbcation, of many ova. There was also a large quantity of infusors 

 and many nematodes among the eggs. 



The larvtfi do not appear to have developed much too rapidly. The 

 cooling was doubtless not sufficiently low. I think a slightl}' lower 

 temperature, 34° to 35° F., would not injure the ova and would 

 probably be sufficient to retard the ova for the requisite period. 



Gravel a'lid Glass. 



While the spawn attached to the gravel did very well, that on the 

 glass could not be said to be distinctly inferior. Glass plates are 

 much more easily handled and with their aid a larger cjuantity of ova 

 can be dealt with. The spawn on the gravel was less in quantity, 

 less crowded, and its situation on small pieces of stone permitted, 

 possibly, a more effective aeration. 



Exposure to Light: Growth of Diatoms. 



A danger which was apparent during this experiment has, I believe, 

 a greater bearing on the well-being of the ova than their location on 

 glass or gravel. That is, exposure to light. Light has a great 

 influence in stimulating the growth of diatoms as Allant and Nelson 

 show. If deprived of light the culture of diatoms dies off". The 

 quality of the water also affects the growth of diatoms. The two 

 authors point out that in the tank-water of the Pljmiouth Laboratory 

 larger and healthier growths of diatoms were got than in water pro- 

 cured some distance off" shore. This fact was ascribed to the greater 

 quantity of organic matter in the tank-water. 



The diatoms which grow on the ova tend to prevent the aeration of 

 the embrj'o, and are also, I consider, the probable cause of the 

 premature escape of the larvae by hastening the decay of the zona. 

 No doubt deca}' takes place normally during incubation. If that 

 decay be hastened the embryo ma}' be able to burst its way to 

 freedom at a smaller size than the average. 



* The larvae were caught in a trap in which some were killed. 



+ " The Artificial Culture of Marine Plankton Organisms." Quarterly 

 Journal of Microscopical Science, Vol. 55, PI. 2. June, 1910. 



Diatoms attached to the eggs of Lobster, exposed to bright light, caused the 

 decay of the outer egg-membrane. (Auderton) Report of Marine Department, 

 New Zealand, 1908-9. Wellington, 1909. 



