120 Amli/lical Notices of Books. 



animals Is also pointed out, and their resemblances In many par- 

 ticulars to the more perfect of the Vertebrata are traced with 

 some detail. That, though usually minute, they occasionally 

 exceed In size animals of a higher organization, is shown by a 

 curious table of the comparative magnitudes of insects of the 

 different families. 



The succeeding Letters are devoted to the different states of 

 Insects. The authors combat the hypothesis recently advanced 

 by Herold, that the successive skins of the caterpillar, the pupa- 

 case, the future butterfly, and its parts and organs, except those 

 of sex, do not pre-exist as gsrms, but are formed successively 

 from the rete mucosum by a vis formatrix. Against this they 

 argue at considerable length, and adduce several weighty reasons 

 for the preference they give to the older opinion of Swammerdam, 

 that every caterpillar, at its first exclusion, contains within itself 

 the germ of the future butterfly. Through their succeeding 

 stages of Egg, Larva, Pupa, and Imago, the history of insects Is 

 traced in that attractive style and with that perspicuous arrange- 

 ment which characterize the work. The number of eggs laid by 

 Insects, the moulting of the larvae, the cocoons of the pupae, their 

 transformation, and especially the development of the wing of 

 the perfect Insect from the almost shapeless mass formed by it in 

 its rudimental state, are among the topics most ably discussed in 

 this section. The differences existing between the sexes are also 

 explained with considerable detail. But the most striking novelty 

 in this department, as connected with system, is the extension of 

 the views of Mr. W. MacLeay relative to the analogies borne by 

 the larva; of certain insects to the Ametabolous Annulosa, into 

 other orders besides the Coleoptera, in which alone they had 

 before been extensively developed. In addition to the resem- 

 blances of form traceable between larva; and the Ametabola, 

 many are pointed out between them and the various orders of 

 Crustacea.) the Arachnida, and even Mollusca : on the latter 

 analogy it is however probable that some doubts may be enter- 

 tained. Of the fifteen types of larvae thus obtained, characters 

 and examples are given ; and their occurrence or prevalence is 

 carefully traced, through each of the orders of insects rcspec- 



