WEBB : DI-MYARIAN STAGE OI' THE " NATIVE OYSTER. 



17 



the " sick " 03'sters kindl}' hrouglit to him from time to time, as 

 the lateness and smallness of tlie second " fall of spat " — the first 

 having been destroyed b}- an unexpected spell of cold weather — 

 made it almost useless to attempt the capture of older embryos 

 which had left the parent's shell, though mica plates were pre- 

 pared for the purpose. 



Nevertheless, it was possible to make out in the later 

 '' wliite spat " and in the " black spat," what appears to be a 

 posterior adductor muscle (PI. I., Fig. i, /. add.), which 

 occupies a spot just \entral to the anus, and is indicated, 

 though not labelled, in Professor Huxley's drawing (Figure A). 

 In Horst's Figure \ also, the spot is surrounded by a continuous 

 outline, and appears exen more definitely, but is not mentioned 

 nor described in the letterpress. 



II 



n^add- 



Figure B. The same as figure A, but seen from a point to its south-east. 

 Lettering as before. {Aft:r Huxley.) 



Now, it was not to be expected that the posterior adductor, 

 if present before the attachment of the oyster, would be easy of 

 identification, or it would have been recognised long ago ; but in 

 the light of the Brightlingsea specimens, those at the Ro3'al 

 College of Science were examined through the kindness of 

 Professor Howes. The series there includes a slide made by Dr. 



'■ On the Development of the European Oyster, Ostrca cJuUs, I,." 

 Q. J. Mic. S., n.s., vol. xxii., 1882, plate xxvii., figure 12. 



