82 THE SCIENTIFIC WORK OF THE 



trae were surveyed, and the spawn was found in greatest abundance 

 in the hollowed gravel- covered areas, where for many square yards 

 it formed a layer nearly half an inch thick. The depth at the banks 

 is from seven to thirteen fathoms, while around it, where the bottom 

 is muddy or sandy, it is about twenty fathoms. The relations of 

 salinity and temperature are described, and it is shown that a 

 probable cause of the desertion of spawning grounds may some- 

 times be the loss of full trammel nets, which were found during the 

 survey filled with putrefying fish. The spawning process, and the 

 mode of fertilization, are fully described. It is shown that while 

 the great spawning periods are spring and autumn, spawning goes on 

 to some extent in nearly every month of the year. It is not known 

 how long herring frequent the banks before spawning begins, but 

 they probably remain several days after its commencement ; and the 

 males longer than the females. The appearance of the spawn as 

 naturally deposited is described ; by transferring ripe herring to the 

 tanks in the Rothesay Aquarium, the whole process of spawning was 

 fully studied, and a number of experiments were made as to the 

 influence of currents, light, &c. Professor Ewart artificially fer- 

 tilized and hatched herring ova, hatching occurring in from eighteen 

 to twenty-two days ; a full account of the process is given, and of 

 the habits of the liberated fry.* 



In the Report for 1884, and in that for 1885, Mr. George Brook 

 gives an account of his investigations On the Development of the 

 Herring.-\ The first part consists of a resume of what was already 

 known on the subject, with especial relation to the labours of Kupfi^er, 

 several of whose figures are reproduced. Kupffer's paper, Ueher 

 die Entwichlung des Herings im Ei, is discussed seriatim chapter 

 by chapter, notes from other papers beiug added. In the second 

 paper the results of the investigations carried on at the Rothesay 

 Aquarium with artificially fertilized ova are described. The reten- 

 tion of vitality by sperms and ova after the death of the adult is 

 discussed, and a full description of the developmental phenomena is 

 given. 



In the Report for 1885, Professor Ewart gives an account of 

 experiments carried on as to the Development of Serving Ova in 

 Deep Waterj'l a subject of importance in relation to offshore fishing 

 banks. Herring may spawn normally on the gravel-coated grounds 

 in the North Sea in water from 60 to 100 fathoms deep ; but these 

 banks have never been well examined or surveyed. Professor Ewart 



* See also a paper On the Natural and Artificial Fertilization of Herring Ova, by 

 J. C. Ewart, M.D., Proc. Roy. See, London, 1884. 



t Third Report, pp. 32—50, pi. i, 1885 ; Fourth Report, pp. 31—41, pis. i. ii, 1886. 

 X Fourth Report, pp. 43—46, 1886. 



