178 "t'. S. BUREAU OF FISHERIES 



with a snap without first closinp; the mantle and dart a short dis- 

 tance alontr the bottom, hinge foremost. This process is not re- 

 peated and is not seen often. With this species and in this region 

 swimming would seem to be more a means of protection than of 

 transportation after an early stage of growth. On numerous oc- 

 casions the writer has failed to secure half -grown scallops because of 

 their habit of swimming seemingly for the purpose of escape. 



Fig. 3. — A bay scalloij lying on its right side, with the left valve, left gill, and umsl 

 of the left mantle lobe removed. AM, adductor muscle; B. byssal notch (over- 

 grown by small oyster) ; C, cartilage ; DD, digestive diverticula overlying stomach ; 

 F, foot ; O, gill ; H. hinge ; K, excretory organ or kidney ; MM, mantle margin 

 with eyes and tentacles along outer edge and other tentacles at inner edge ; Pa, 

 palps ; Pe, pericardium ; li, rectum ; VM, visceral mass, containing male and 

 female genital organs and several folds of the intestine 



VISION 



The possession of siglit is hardly less interesting than the ability to 

 swim. The functioning of the numerous, beautiful eyes seems to be 

 limited to the perception of movement. It was observed * that a 

 sudden increase in illumination (as by flashing a light on a scallop 

 when its shell was open at night) produced no effect, but that if an 

 object was so moved that its shadow fell on the eyes of the scallop, 

 the shell was closed quickly. When a starfish was placed in one glass 

 aquarium and a scallop in another adjacent,^ the scallop, although its 



* See Memoir on I'ecten. by W. .1. Dakin, Appendix, Report for 1908, Lancashire Sea- 

 fisheries Laboratory, Liverpool. 1900. 



^ See Studien tJber den Tons. VI. Die Pilgermuschel, by J. von Uexkull, 112. Zeit. 

 Biol., .58. 



