144 TIIURLOW C. NELSON. 



covers more than one half of the outer surface of the left valve, 

 extending from close to the anterior ventral edge almost to the 

 umbo, but falling short posteriorly. From his study of the 

 byssus gland in the base of the foot of the larval oyster, Stafford 

 concluded that this organ must furnish the substance used to 

 attach the larva, since the large amount of this material and its 

 position far under the left valve preclude the use of the mantle 

 for this purpose. 



It has been my good fortune to observe the actual attachment 

 of oyster larvae under semi-natural conditions, and thus to be 

 able to fill the gap in the information about this process. -Large 

 numbers of full grown oyster larvae were found at 8 P.M., July 

 23, in the water surrounding our laboratory houseboat on Barne- 

 gat Bay. A glass plate measuring 3x4 inches was lowered ver- 

 tically into the water and removed half an hour later, and imme- 

 diately suspended horizontally in a dish of sea water under the 

 binocular. 1 



Six oyster larvae were moving about over the glass, holding 

 on by means of the very active and highly adhesive ciliated foot. 

 Some were on the upper, others on the lower side of the glass, 

 thus permitting observation of the attachment process both from 

 above and from below. With the velum withdrawn, and slowly 



B 



FIG. i. Illustration of the method of creeping of the oyster larva over a glass 

 surface. -4, larva with foot fully extended; B, larva with foot contracted and 

 body pulled forward. Larvae shown from the right side. 



rolling the shell from side to side, the larvae extended the foot to a 

 distance of about 0.25 mm., attached the distal end and then a 

 contraction of the foot pulled the body forward. The "heel" 

 of the foot next being attached, the body was swung part way 

 around; the tip of the foot was again extended in the new direc- 

 tion and the process repeated (Fig. i). When first observed at 



1 Jackson, '88, J. Nelson, '08, and Stafford, '10, used this method of obtaining 

 oyster spat; but no one of these authors records having witnessed the actual attach- 

 ment of the larva. 



