20 THE SCALLOP FISHERY 



the arrangement of the yolk granules within the egg. A light color ap- 

 pears to be caused by large vacuoles or clear spaces among the yolk 

 granules, as are often found in distorted and immature eggs. Evidently 

 the number, size and arrangement of these vacuoles in respect to the 

 granules determine the color of the mass, and thus indicate the maturity 

 or immaturity of the eggs. Orange-colored ovaries when placed in 75 

 per cent, alcohol in a short time become white, the orange color being 

 extracted by the fluid. 



The Spermatozoon. --The spermatozoon or male cell (Fig. 2) is 

 extremely minute, being only an exceedingly small fraction of the size 

 of the egg. It consists fundamentally of two parts, an elliptical head 

 and a slender whip-like tail, which is used as an organ of locomotion 

 in seeking the egg. The size of the head is ^eo by %oo of a millimeter 

 (%soo by Mssoo of an inch), with a tail about }o of a millimeter 

 (%oo of an inch) in length. The minute anatomy was not studied. 



Spawning. - - The terra " spawning " refers to the discharge of the 

 eggs from the female or the spermatozoa from the male. With most of 

 the lamellibranchiate mollusks, the class to \vhich the scallop belongs, 

 it is the act of throwing off the sex products, which meet in the water for 

 the purpose of fertilization. Pecten irradians, as is often the case with 

 highly specialized mollusks, is hermaphroditic, i.e., both sex elements are 

 found in the same individual. Spawning in this instance is the dis- 

 charge of either eggs or spermatozoa from the same animal, usually 

 at different times. 



In the Pectinidae the opening from both ovary and testis lead into a 

 common duct with a single orifice, which opens into the kidney com- 

 paratively near its external aperture. Pelseneer (9). The sexual 

 products, as they are extruded, pass through a part of the kidneys just 

 dorsal to the large adductor muscle into the mantle chamber, where 

 they are discharged into the water. The discharge takes place through 

 the pseudo-siphon, formed by the mantle when closed, at the right or 

 posterior edge of the shell, as the animal lies in a natural position. 

 The spawn is usually cast forth as a fine spray by a quick snap of the 

 valves and is rapidly diffused through the water, though sometimes the 

 valves remain quiet, the spawn then passing out in a steady stream. 

 As the mantle fringe is slightly opened to allow the spawn to roll gently 

 out, this latter method can be compared to the exhaling of tobacco smoke 

 from the human lips. If eggs are given off they either appear in pink 

 masses or are just visible to the naked eye as fine white specks, making 

 it possible for the observer to readily distinguish them from the sperma- 

 tozoa, which give to the water a quivering, milky appearance. The 

 amount of eggs extruded at one time varies considerably, but generally 

 numbers high in the thousands and even millions. 



The following observations upon Ihe spawning of individual scallops 

 were made at Monomoy Point. The scallops were confined, as described 



