336 Professor Huxley [May 11, 



WEEKLY EVENING MEETING, 

 Friday, May 11, 1883. 



George Busk, Esq. F.R.S. Treasurer and Vice-President, in the Chair. 



Professor Huxley, LL.D. F.R.S. 

 Oysters and the Oyster Question. 



[The whole discourse, with additions, is printed in the October and November 

 numbers of the ' English Illustrated Magazine,' published by Messrs. Macmillan.] 



The oyster possesses representatives of all the most important organs 

 of the higher animals, and is endowed with corresponding functions. 

 The " loves of the oyster " may be mythical, and we may even be 

 sceptical as to its parental tenderness ; but no parent can take 

 greater care of its young. And though the oyster seems the type of 

 dull animal vegetation in its adult condition, it passes through a vaga- 

 bond, if not a stormy youth, between the time in which it is sheltered 

 by the parental roof, and that in which it "ranges itself" as a grave 

 and sedentary member of the oyster community. It has a shell com- 

 posed of two pieces or valves, the one of which is thick and has a 

 convex outer surface, while the other is thinner and flattened. The 

 contour of each valve is irregularly oval, with a small end, which 

 usually presents a triangular prominence known as the umbo or beak 

 (um.) (Fig. 1), and which answers to the back or dorsal region of the 

 animal. When this is turned upwards, the opposite or ventral margin 

 is seen to be evenly curved, and to be gradually continued into the 

 curved line of the front margin [ant.), while the hinder margin (post.) 

 is usually straighter. By attention to these characters, the right 

 valve can always be distinguished from the left ; but, in the great 

 majority of cases, it is more easily known because it is the flat valve. 

 If the oyster is fixed, it is the convex valve which is attached ; and 

 free oysters naturally lie on this valve, inasmuch as the other is the 

 lighter, and the more easily raised by the mechanism which will be 

 presently described. 



The exterior of the shell is rough and usually of a brownish-green 

 colour. It is marked by lines, which ran approximately parallel 

 with the contour of the shell, around a common centre placed at the 

 summit of the umbo, and indicate the successive layers by the apposi- 

 tion of which the shell has been deposited upon the skin of the 

 animal. The inner face of each valve has the well-known white and 

 opaline or iridescent aspect which appertains to nacre or mother-of- 

 pearl, except the flattened or concave surfaces of the umbones, which 

 are marked by parallel lines answering to the lines of growth on the 



