130 THE SCALLOP FISHERY 



abnormal development, non-fecundation of the numerous immature eggs, 

 and sacrificing the parent. The other method (forced spawning) is 

 accomplished by transferring the scallops from cool to warmer water, 

 which causes the ripe eggs to be extruded in a more natural manner. 

 Spawn could be obtained at any time during the season if the tem- 

 perature was satisfactory, and the same scallops could be used over 

 and over. 



In raising the Iarva3 for laboratory study the aquaria should be 

 kept clean, a relatively large amount of water for a few larva? should 

 be allowed, as crowding results in death, and the decomposing eggs, 

 if not separated by siphoning off the surrounding embryos, soon cause 

 the death of all. With every precaution the death rate is very high, 

 owing to the debris, parasitic protozoa, bacteria, etc., which collect 

 in the water, but there is good reason to believe that by careful experi- 

 ment scallops can be raised in numbers in the laboratory, although 

 during this investigation only a few were successfully carried to the 

 post-embryonic stage. 



Artificial Propagation. - - The object of artificial propagation is 

 the prevention of the great " infant mortality," as under natural con- 

 ditions but %o,ooo of 1 per cent, of the number of eggs develop into 

 mature scallops. Artificial fertilization and the protection of the 

 young embryos during the first few days of life would to a large extent 

 do away with this great loss; but the practical difficulties in success- 

 fully rearing the larva? over this period are such as to make the under- 

 taking problematic. At the present time liberation of the eggs imme- 

 diately after artificial fertilization seems to be of most benefit to the 

 fishery. 



The Rate of Growth. 



Methods of measuring the Scallops. - - Three measurements were 

 made of each scallop (Fig. 65) : (1) height, along the dorso-ventral 

 axis, or from the hinge to the opposite edge of the shell; (2) width, 

 along the antero-posterior axis, or from the left to right edge of the 

 shell; (3) thickness, along the lateral axis, or the depth through the 

 valves. 



The growth of any mollusk can only be accurately stated by deter- 

 mining the gain in volume. As it was obviously impossible to obtain 

 the water displacement of the scallop with its loose shell, the following 

 method of calculating the volume was devised : the three dimensions 

 of the scallop were multiplied together and the result called the cubic 

 volume, equivalent to the volume of a solid rectangular prism of 

 those dimensions, in which the scallop is theoretically enclosed. Thus 

 the following proportion can be established: scallop A of cubic vol- 

 ume 1,000 is to scallop B of cubic volume 5,000 as 1,000 is to 5,000 

 ( A :B:: 1,000:5,000). Thus scallop B is five times, or 500 per cent, 

 larger than scallop A, and the relative per cent, of increase is ob- 





