February 6, 1896] 



NATURE 



323 



who has ransacked it in a way that it would have been 

 hop>eless to attempt without the preparation gained by 

 many years' work in connection with the Zoological 

 Re con. 



His style is graphic and pleasant and, even when he is 

 most erudite, he is never dry. Nevertheless, the book 

 will appeal with more force to the expert than to the 

 beginner. The definitions are often vague, notably in 

 the chapter on external structure. This arises less from 

 any fault in the authors method than from a reluctance 

 to give definitions which do not embrace all known 

 variations from a common type. To those who can read 

 between the lines this vagueness presents no difficulty, 

 but we suspect that the general reader will fail sometimes 

 to get a clear conception of the subject. The in- 

 sufficiency of our present knowledge is a favourite and 

 over-emphasised text of the author, who does not conceal 

 his dislike both to generalisation and the acceptance of 

 morphological axioms. Though he rarely expresses his 

 opinion, even on matters where it would be most wel- 

 come, in a remarkable footnote (p. 91) he suggests that the 

 wings, equally with the legs, are " appendages." He might 

 be thought to protest against the limitation of the term to 

 a single homologous series, but his remarks on the pos- 

 sibly duplex origin of the thoracic somites tend to negative 

 this view. That there can be any homology between the 



Fig. 2. — Front leg of the mole-cricket, a, outer ; b, inner aspect ; ^, ear-slit. 



legs and wings is a dangerous suggestion to hint at in a 

 work not intended solely for critical readers. 



Where so much is novel, it is impossible, within the 

 limits of a notice, to touch on even a small part of the 

 subjects dealt with in the work : the development of the 

 antenniE in Forficulidcr, the mimetism of Mantida:, the 

 economy of the Termites, the insects of the coal-measures, 

 the formation of galls, these are examples of many topics 

 discussed in the light of the most modern researches. 



The chapters in this volume treat of external and 

 internal structure, development and classification, and, 

 out of the nine orders proposed, of the Aptera, Orthoptera, 

 Neuroptera, and part of the Hymenoptera (Sessiliventres 

 and Parasitica). The remaining orders will occupy 

 vol. vi. of the series. 



Of the chapter on development the most suggestive 

 part is that on metamorphosis. Dr. Sharp urges that 

 this phenomenon is yet very imperfectly understood, 

 owing to our ignorance of the underlying physiological 

 changes, and that nothing can be postulated about 

 it without taking into account the processes of em- 

 bryonic development and of such deviations from the 

 normal course as hypermetamorphosis and the extra- 

 ordinary changes undergone, for example, by parasitic 

 Hymenoptera. The view that ecdysis is correlated solely 

 with growth, is rejected in favour of Eisig's suggestion 

 that it is a means of excretion, 



NO. I371, VOL. 53I 



It follows that metamorphosis is here regarded as of 

 subordinate importance in classification, and though the 

 usual definitions of its extent are rejected, no alternative 

 scheme on a physiological basis is proposed. It is quite 

 unlikely that entomologists will adopt the author's ex- 

 treme views, but these pages, the result of much thought, 

 will come as a surprise to those who have a comfortable 

 belief in the fixity of the accepted degrees of metamor- 

 phosis, degrees which, as Camerano has said, are purely 

 scholastic. 



Sexual phenomena, such as heterogamy or dimorphism, 

 are treated only in connection with the forms which 

 exhibit them, but at the end of the chapter on internal 

 anatomy there is a short paragraph on parthenogenesis 

 and pjedogenesis. It is nowhere indicated that the latter 

 is an extreme form of the more general phenomenon of 

 neotenia, alluded to under the Termitida. 



Little importance is attached to the threadbare 

 question of the division of the class into orders, and in 

 the arrangement here adopted for convenience and 

 without discussion the undue complexity of some recent 

 systems has been, we think, wisely abandoned. Nine 

 orders are indicated : the Neuroptera include the 

 Pseudoneuroptera and Mallophaga, and two small orders 

 only are kept separate, the Aptera (for Thysanura^and 



Fig. 3. — Panorpa communis, male. Cambridge. 



Collembola) and the Thysanoptera. The extension of 

 Neuroptera to its original limits is in accordance with 

 the views of some recent writers, for example, Brong- 

 niart. But with respect to the Aptera, which is coter- 

 minous with Brauer's Apterygogenea, attention has not 

 been paid to Grassi's recent admission that the Thy- 

 sanura, in common with all existing insects, may be 

 derived from winged forms. They present many 

 primitive features, but these are compatible with their 

 place as the lowest Orthoptera, the homology of the 

 abdominal styles with the legs having been lately 

 seriously questioned. Though the inclusion of the 

 Mallophaga in Neuroptera is not new> it is a pity that no 

 reasons are given for an association which, however 

 sound, is hard to appreciate. 



Of the variety of subjects in the chapters on the 

 separate orders, we have already spoken. The Hymen- 

 optera, being more homogeneous, are treated in some- 

 what less detail than the others. A figure of some of the 

 manifold forms assumed by the petiolate abdomen would 

 have been welcome, and among structural points there is 

 no reference to the strange nipper-like front tarsi of 

 Gonatopus. 



In the chapter on Acriditdce, no mention is made of 

 the fact, important in connection with the migratory 



