148 



Part III. — Thirteenth Annual Report 



during the night and even oftener during the day, I daresay the results, 

 as far as depending on the constant temperature, are almost accurate. 



On the 15th of March I received eggs of three species : cod (G. 

 morrhua), haddock (Gr. (eglefinus), and whiting (G. merlangus). They 

 had all been artifically fertilised by Mr Liston, the mate of the ' Garland,' 

 who was out on a trawler to collect spawniug plaice for the hatchery, 

 and they were brought to Dunbar by the 1 Garland.' The eggs on their 

 arrival were all in an early stage of development, the second segmentation 

 being completed in the whiting eggs ; the others were not quite so far 

 advanced. The eggs were divided into jars holding water of the same 

 temperature in which they arrived (3° C.), and the jars transferred to 

 the different spaces in the hatching apparatus, where the temperatures 

 had been already fixed as follows : - 2°, - 1°, 0°, + 1°, 2°, 3°, 4°, 5°, 6°, 

 8°, 10°, 12°, 14° C, the corresponding figures, according to the Fahrenheit 

 scale, being:— 28-4, 302, 32*0, 33'8, 35-6, 37*4, 39*2, 41-0, 42 8, 46-4, 

 50 # 0, 53 6, 57 '2° F. In this way the water in which the eggs were 

 placed was gradually cooled or heated till the temperature reached the 

 proper level. 



As I had three species, and thirteen specimens were taken of each, 

 there were thirty-nine bottles with eggs under observation at the same 

 time. 



The water was refreshed daily, and in order not to expose the eggs to 

 a change in temperature while this was being done, a large jar, with 

 clean spare water, was constantly kept in each room, so that it at any time 

 had the proper temperature. The old water in the bottles and any dead 

 eggs were removed by means of a syphon. 



The eggs were also occasionally removed from the jar, and the latter 

 thoroughly cleansed. This is a matter of great importance, in order to 

 secure a satisfactory result when hatching is carried out in water that is 

 only occasionally refreshed. 



As to the time of incubation at the different temperatures, the result 

 will be seen in the following table, which also includes plaice and 

 flounder, the eggs of which I fertilised artificially at Dunbar. 



The hatching of all the eggs of one species does not take place at the 

 same time, even if the eggs are from the same female and dealt with 

 in the same way. This difference in time varies from a few hours to 

 several (3 or 5) days. 



In regard to the eggs of the plaice, I took particular account in some 

 cases, as will be seen in the following table : — 



Table L — Showing the Difference in the Time of Incubation of Eggs, 

 taken from one Plaice, at a Temperature of 8°, 10°, and 12° C. 





Hatching Period. * 







1st day. 



2nd day. 



3rd day. 



4 th day. 



5th day. 





8° C. 

 10° 

 12° 



1 



9 

 2 



1 



29 

 4 



14 

 10 

 7 



10 

 2 

 17 



35 

 4 



1 Number 

 1 of eggs 

 J hatched on 

 I each day. 



* The ' 1 hatching period " includes the time from the emergence of the first to 

 the emergence of the last embryo, in a batch. 



