SCALLOP INDUSTRY OF NORTH CAROLINA 179 



enemy stood before it, gave no reaction until the starfish moved. Tlie 

 scallop then thrust out its long sensory tentacles to investigate. Ex- 

 perimental study of the vision of scallops is difficult because the 

 animal quickly becomes accustomed to stimuli and fails to respond. 

 It is reasonable to .suppose that vision has been developed or im- 

 proved in connection with the ability to swim, which would render it 

 especially useful for protection. 



FEEDING 



Scallops, like oysters, clams, and other bivalve moUusks, feed upon 

 minute organisms obtained from water drawn into the shell. The- 

 active beating of the minute, hairlike cilia on the gill filaments pro- 

 ducer water currents that, when the shell is open, cause a steady 

 circulation of water into the shell, through the gills, and out of the 

 shell. The gills strain food from the water, pass it to the palps, 

 through which it is drawn, still by ciliary currents, into the mouth, 

 esophagus, and stomach. 



BREATHING 



Respiration or aeration of the blood occurs not only in the gills 

 but also in the mantle lobes, which are very thin and well supplied 

 with blood vessels. Both gills and mantle are bathed with the cur- 

 rent of water drawn in by the action of gill cilia. 



REPRODUCTION 



k 



In the bay scallop both sexes are present in one individual. Eggs 

 and sperms are to be found in the tissue of the visceral mass, but in 

 separate areas. In mass, the sperms are white or cream colored, 

 the eggs pink or even red. To observe the gonads it may be neces- 

 sary to rub otf the epithelium, which often is pigmented so heavily 

 as to obscure the underlying tissue. Although the writer has se- 

 cured, experimentally, the fertilization of eggs of one individual 

 by sperms of the same individual, it is supposed that self-fertilization 

 occurs seldom. Spawning may be considered to be autumnal, al- 

 though it begins as early as midsummer and continues as late as 

 January. Both eggs and sperms are cast into the water, in which 

 the eggs drift and the sperms sswim actively. When a sperm comes 

 in contact with an egg, fertilization occurs and development begins. 



DEVELOPMENT 



After fertilization, the minute egg, about three-thousandths of an 

 inch in diameter (0.08 millimeter), divides and becomes a 2-celled 

 embryo. In a few hours repeated divisions develop a complex mass 

 of ceils, the outer of which possess cilia that, by their beating, cause 

 the embryo to swim about. Soon after this a primitive mouth 

 appears at one end and a whiplike appendage at the other. This 

 stage may be attained in less than a clay. Development up to this 

 point has been wholly differentiation. No outside nourishment has 

 been secured and no growth made. 

 18635— 2S 2 



