126 NATURAL SCIENCE [August 



development of insects within the egg. But it is surprising to find 

 no reference whatever to parthenogenesis ; the fact that reproduction 

 by virgin females is common in certain insects is now widely known, 

 and some discussion of the subject might be expected even in a much 

 more elementary work than this. Nor is there any mention (except 

 incidentally on the last page of the book) of the fact — most suggestive 

 in its bearing on the possible origin of degenerate groups — that some 

 insects become sexually mature in the larval stage. It is hard to 

 understand what considerations can have led to such omissions as 

 these. 



The concluding part of the book deals with metamorphosis, and 

 contains a short summary of the external forms assumed by larvae 

 and pupae, and of the development of the imago from the earlier 

 stages. The structure of the typical larvae in the great orders is by 

 no means fully described ; but there is a more detailed description of 

 those interesting forms which pass through what is called a " hyper- 

 metamorphosis." The formation of the adult organs in Lepidoptera 

 and Hymenoptera from the imaginal discs is described in detail, 

 while a special section is devoted to the corresponding phenomena in 

 the Diptera which have been studied better than any other order in 

 this connection. Prof. Packard considers the campodiform larva to be 

 more primitive than the eruciform, and figures a series of beetle grubs 

 which show the transition from the one to the other. In a final 

 chapter the fascinating question of the origin of metamorphosis is 

 discussed ; and the author comes to the conclusion that the trans- 

 formations which now characterise all the higher insects have been 

 acquired since the group obtained the power of flight. 



A very valuable feature of the book is the full bibliography 

 appended to each section ; by means of this the student will be 

 enabled to follow up any subject on which he desires further informa- 

 tion. The figures are numerous, and as a whole good. Though the 

 execution is, in some cases, rough, comparing unfavourably with the 

 beautiful drawings in the Cambridge Natural History, for instance, 

 only a few, such as the larva of Eristalis on p. 430, can be considered 

 unworthy of the book. Altogether the work supplies a long felt 

 want, and all serious students of insects should be grateful to Prof. 

 Packard for having given them in a single volume so full a summary 

 of what is known about insect structure and life-history. 



Geo. H. Carpenter. 



Essex Vertebrates 



The Mammals, Reptiles, and Fishes of Essex : a contribution to the Natural 

 History of the County (Essex Field Club Special Memoirs, Vol. III.). By Henry 

 Laver, M.R.C.S. . &c. 8vo, pp. 1-138, with 8 full-page illustrations. Chelmsford: 

 E. Durrant & Co. ; London : Simpkin, Marshall & Co. 



For many years the attention of those fortunate naturalists who live 

 in the country and have opportunity to observe nature at home has 

 been largely devoted to birds, as is indeed natural from the readiness 

 with which those creatures are seen and studied, and their own extreme 

 attractiveness. It thus happens that while nearly every county in 

 the British Isles possesses a popular work on its birds, the other 

 vertebrates have been very largely neglected. 



