848 The Zoologist— August, 18C7. 



arrested in her compulsory course, deposits her eggs in little crevices 

 of the bark, or, as some authors have said, in the axils of the leaves, 

 and these eggs remain unhalched until the following spring or summer; 

 they then produce a race entirely different from the parent, a race 

 without wings, of different structure, different colour, eating a different 

 food, and bearing a different name. Thus Aphis Humuli of the autumn 

 may have wings, a well-developed mesothorax, a distinguishing colour, 

 an oviparous mode of reproduction, and may feed exclusively on the 

 juices of the hop ; while its descendant, Aphis Pruni of the spring, will 

 have no wings, no developed thorax, a different colour, a viviparous 

 mode of reproduction, and will feed exclusively on the sloe. The 

 account reads marvellously like a fable, but it is not so : Mr. Walker, 

 who has thoroughly investigated the subject, knows that these things 

 are so; and this not by chance or by accident, but by a fixed law from 

 which there is no appeal. 



I feel that the subject is rather indicated than exhausted in these 

 cursory remarks, but I refrain from amplification: what I have adduced 

 is incontrovertible, and must suffice ; and I am sure you will sec its 

 important bearing on our systematized lists of species, which must be 

 decimated when life-histories yet unknown are carefully worked out. 



You will perhaps ask, are these laws of atavism and avism universal 

 or exceptional ? The query is germane to the matter under con- 

 sideration, and must be met, but I will give a very modified and 

 rather indefinite reply. May I illustrate my meaning by an example? 

 1 believe it a law that the four extremities of all endosteate animals 

 shall terminate in five divisions, as in Man ; but I know that in very 

 many instances the exceptions are so numerous and so decided as to 

 eclipse or conceal the rule ; as, for instance, in our horses and cattle. 

 So in atavism or avism I cannot doubt the universal prevalence of the 

 law, although I am fully aware how generally it is obscured by 

 exceptions which appear to be conflicting. 



Believe me, dear Mr. Wollaston, 



Most truly yours, 



Edward Newman. 



PS. T have to acknowledge, with thanks, ihe receipt of a communication from 

 Mr. Wallace, in reference to Letler I., but to say I must decline to publish any 

 comments on this series of Letters until my readers are enabled to judge of them as a 

 whole. I have also to apologize for a typographical error at p. 725; in the second and 

 third lines the word "Kuchelia" occurs: the first is correct, the second should he 

 "Cheloaia."— B. N. 



