Royal Society. WJ 



deep umbilicus, which invariably characterizes O. acuta in every 

 variation and stage of growth. 



I am. Gentlemen, 



Your most faithful Servant, 



J. GwYN Jeffreys. 

 1 Montagu Square, London, 

 May 1859. 



P.S. Since the above was written, I have received a letter from 

 my friend Mr. Alder, which contains some remarks so apposite and 

 valuable, on the presumption of specific distinction in animals which 

 live together but differ from each other in form, that I will, with his 

 permission, transcribe them. Mr. Clark's ideas on this subject will 

 be found at page 408 in last month's number of the 'Annals.' 

 Mr. Alder says — "The argument from two forms li\nng together 

 under the same circumstances, is good, I think, as a presumptive 

 proof that they constitute distinct species. The general idea of a 

 species is, that the individuals are the progeny of a common stock, 

 freely breeding together, and producing their like in uninterrupted 

 succession, without mixing with other species (at least in a state of 

 nature). If, therefore, two nearly allied forms live together under 

 the same circumstances, without showing any intermediate forms, 

 the presumption is that they are specifically distinct. This, I think, 

 is a fair argument, resting on the belief that mere varieties will breed 

 together when they come in contact, and that they are generally the 

 result of different external circumstances, and gradually return to the 

 typical form when those circumstances are removed." 



PROCEEDINGS OF LEARNED SOCIETIES. 



ROYAL SOCIETY. 



December 9, 1858. — Sir Benjamin Collins Brodie, Bart., President, 

 in the Chair. 



" On the Ova and Pseudova of Insects." By John Lubbock, Esq., 

 F.R.S., F.L.S., F.G.S. 



In the 'Philosophical Transactions' for 1857, I endeavoured to 

 show that the agamic eggs of Dajj/mia are formed upon the same 

 type, and consist of the same parts, as any other egg. My object 

 in undertaking the investigation, of which the present paper is the 

 result, was to determine whether the same held good of the agamic 

 eggs or pseudova o{ Coccus, Ci/nips, and other insects. This inquiry 

 was the more interesting, because Prof. Huxley had found several dif- 

 ferences between the ovarian products of the oviparous and vivipa- 

 rous Aphides ; and because, according to Prof. Leydig, the develop- 

 ment of the pseudova in Coccus was extremely peculiar. 



My examination of Coccus was concluded, and the results com- 

 mitted to paper, in the early part of June last ; but I then found that 

 so little was known, especially in this country, about the develop- 



32* 



