i6 



WF.RB : DI-MVARIAN STAGE OF THF. 



OYSTKR. 



Seven years later Dr. Robert Tracy Jackson' described and 

 figured a sta<^e in the American oyster, in wliich the two muscles 

 (Fig. C, a. add. and />. add.) were clearly to be made out. The 

 embryos in question were examined after attachment, in tlie case 

 of the experiment, on a strip of glass, which had been exposed in 

 an earthenware drain-pipe partially sunken in the sand at low- 

 water mark. No spat growth had taken place. 



Last summer, when the writer had the privilege of working 

 in the Marine Biological Laboratory' which the County Council 

 of Essex fitted up at ?]rightlingsea in connection witli some 



\ *1 



Figure A. An embryo of tfie European oyster, Ostmx cdidis, L., seen in 

 optical section from tlie left side. a. add., anterior adductor muscle ; an. anus ; 

 /(. hinge of shell; /. intestine ; /./. ;-./. left and right lobes of the "liver;" 

 ce. oesophagus ; r.s. r.i. superior and inferior muscles, which retract the velum ; 

 St. stomach ; !■. velum, with its long cilia. {After Huxley.) Reprinted from' 

 the English Illustrated Maga-iue. 



experiments in Oyster Culture, he betliought himself of the 

 di-myarian stage, but had to content himself with larvse from 



■The rhylogcny of the Pelecypoda," by Robert Tracy Jackson, Mem. Boston Soc. Nat 

 Hist., vo!. IV., 1890, p. 300, pi. xxiv., figs. I and 2. N.B.-The discovery of the di-myarian 

 stage was announced \n Proc. Bost. Soc. Nat. Hist., vol. xxiii. (1888). 



