297 



NOTE ON THE ANATOMY OF THE LAKVA OF THE EUROPEAN 

 OYSTER, OSTREA EBULIS, Linx. 



By Mahtin F. "Woodward, Demonstrator of Zoology, 

 Royal College of Science. 



Bead May IQth, 1895. 



PLATE XX. 



Ever since Huxley ^ first pointed out that the single adductor muscle 

 of the "black spat" larva of the oyster was the anterior adductor, 

 and therefore not the morphological homologuc of the single muscle 

 of the adult, which is the true posterior adductor, students of lamelli- 

 branch anatomy have awaited with anxiety the discovery of the 

 di-myarian stage which Huxley had practically prophesied. 



Our patience was at length rewarded, for in 1888 Jackson described 

 the true and xmdoubted di-myarian stage for the American oyster, 

 0. Virginianar' An examination of his figures will at once show the 

 reason why Huxley ^ and Horst ^ were unable to find the stage, their 

 specimens being in the black spat stage, still within the shell of the 

 parent, while Jackson's di-myarian stage was a recently attached 

 young oyster, with a disappearing velum and well-developed gills. 



The most recent contribution to this subject is a short note by 

 Mr. W. M. AVebb ■* : this is a description of a supposed di-myarian stage 

 in the "native" oyster. 



Mr. Webb's material consisted of preparations of white and black 

 spat obtained at Brightlingsea, which showed very little beyond the 

 alimentaiy canal, his most important observations being based on the 

 brief study of two slides of black spat belonging to the Royal College 

 of Science, one being a preparation made by Horst and the other by 

 Huxley, these slides being the material from which Huxley's figures 

 (probably composite ones) were made. 



From this material Mr. Webb has constructed a figure* which, 

 if examined alone, would leave no doubt in the mind of anyone, 

 that he had discovered the di-myarian stage in the native oyster. 

 Fortunately, in his description he is not quite so positive as in the 

 figure, but he comes to the conclusion that he has discovered the 

 " incipient condition " of the posterior adductor muscle. Now as these 

 actual specimens had been examined both by Horst and Huxley, or 



1 The English lUustrated Mag. 1883, p. 112. 



2 Proc. Bost. Soc. Nat. Hist., vol. xxiii, 1888, p. 531 ; also Mem. Bost. Sec. 

 Nat. Hist., vol. iv, 1890, p. 300. 



3 Quart. Joum. Micro. Sci., vol. xxii, 1882, p. 311 ; and Tijdschr. der Ned. 

 Dierk. Ver. Suppl. Deal, i, p. 6, fig. 16, 1883-84. 



•^ Journ. Malacol., vol. iv, 1895. 

 5 I.e., pi. i, fig. 1. 



