NATURAL HISTORY OF THE BAY SCALLOP 
603 
stage in 17-40 hours, the writer in 42-48 hours at about 25° C. The anatomy of the 
early veliger, including early shelled larvae, was figured in considerable detail by 
Belding. Besides the structures mentioned, anterior adductor and velum retractor 
muscles are shown. 
Beyond an early “straight-hinged” stage Belding did not succeed in rearing 
the larvae nor, among the forms taken in the plankton net, was he able to recognize 
Figure 21. — Early development: a, Polar bodies formed at animal pole; 6, yoke lobe formed at vegetative pole; 
c, first cleavage; d, 4-cell stage; e, 8-eell stage; /, ciliated gastrula; (a-f, embryonic stages); g, troehophore ( a-g , 
after Belding); h, early veliger or prodissoconch, about 0.08 millimeter long; late prodissoconch, about 0.18 
millimeter long (g-i, larval stages, see text); j, longisection of very early postlarva about 0.22 millimeter long, 
showing asymmetrical, nepionic shell growth; k, length 0.54 millimeter; l, length 1.2 millimeters O'-f, nepionic 
stages); m, transition stage, 1.6 millimeters long, showing byssal notch and teeth, ribs, and overhanging large 
umbo of left valve (drawn with right valve uppermost). Structures: A, Anus; A. A., anterior adductor 
muscle; A. M., adductor (posterior) muscle; O. D., digestive diverticula; E, eye, one of six shown; F., foot; 
FL, flagellum; O., gill; H., heart; M, mouth; Pa., palps; P. A., posterior adductor muscle; P. M., primitive 
mouth; R., rectum; St., revolving stomach contents presumably turned by style; T., tenacles; V., velum 
later stages, short of the fully developed prodissoconch. This stage he figured in 
considerable detail, showing it as about 0.18 millimeter long and with the left valve 
decidedly larger. 
My own attempts to rear the larvse did not take them beyond the straight-hinge 
stage even though they remained alive in this stage for several days. From exami- 
