December 15, 1923] 



NATURE 



857 



has the highest authority, but, so far, the writer has 

 heard of no one who has made and published a detailed 

 comparison between the bones of neolithic Britons and 

 those of modern Somalis and Egyptians. It is highly 

 desirable that an investigation of this kind should be 

 made, for it is difficult to believe that there is any 

 degree of Somali blood in modern England. 



Arthur Keith. 



The Orders of Insects. 



Manual of Entomology : with Special Reference to 

 Economic Entomology. By Prof. H. Maxwell Lefroy. 

 Pp. xvi + 541 + 4 plates. (London: E. Arnold and 

 Co., 1923.) 355. net. 

 '"T^HE classification of insects has passed through 

 X many changes, and most of the systems proposed 

 have been primarily based upon characters afforded 

 by the wings, mouth-parts, and metamorphoses. 

 During the last fifteen years entomology has suffered 

 from an over-exercise of the analytic faculty on the 

 part of morphologists. One result of their activities 

 is seen in the increasing number of subdivisions of the 

 class Insecta, and some eminent authorities even dis- 

 member the latter as a whole. The tendency is to 

 emphasise differences rather than the features which 

 groups reveal in common. In some cases the same 

 morphological characters in different orders are not 

 ( redited with proportional values. The result, as 

 might be anticipated, is a dondition of instability with 

 no very clear conception of what is to be regarded as 

 an order and what is not. 



The foundations of the modern classification of 

 insects were laid by Brauer in 1885. He recognised the 

 fundamental division of the Insecta into the two 

 sub-classes Apterygogenea (Apterygota) and Ptery- 

 gogenea (Pterygota) — members of the former being 

 primitively apterous and those of the latter winged, or 

 in some cases secondarily apterous. Brauer also did 

 much towards dividing the old assemblage Neuroptera 

 into separate sections, each of ordinal value. In 1899 

 Sharp established a system partly modelled upon that 

 if Brauer, and he introduced the terms Exopterygota 

 nid Endopterygota, in order to discriminate between 

 I hose orders in which the wings develop outside the 

 body, and those in which they remain internal until 

 :)upation. He further introduced the term Anaptery- 

 ^i)ta to include those apterous orders which have, 

 presumably, become secondarily wingless. This latter 

 step, however, has the disadvantage of bringing together 

 distantly related groups. 



In 1904 Shipley adopted Sharp's system almost in 

 its entirety, but proposed certain new ordinal names 

 with the double object of doing away with the use of 



NO. 2824, VOL. I 12] 



family designations for ordinal purposes, and of intro- 

 ducing a system in which the suffix " ptera " is extended 

 to all orders. In the same year Bomer proposed a 

 system which recognised the same orders as Shipley 

 (although not necessarily under the same names), with 

 the exception that he adopted a threefold division of 

 the Apterygota, and revived the ordinal name Cor- 

 rodentia for the Psocoptera and Mallophaga. Four 

 years later Handlirsch launched a revolutionary 

 scheme : he no longer retained the Insecta as a primary 

 division of the Arthropoda, and his system involved 

 their dissolution into four classes comprising no less 

 than 34 separate orders. In America he has found 

 support from Brues and Melander (1915), who added 

 the more recently discovered orders Protura and 

 Zoraptera and, at the same time, elevated the family 

 Grylloblattidae to ordinal rank, thus recognising 

 altogether 37 orders. Berlese, on the other hand, 

 in his encyclopaedic treatise " Gli Insetti " reverts to a 

 simplified taxonomy and diagnoses but nine orders. 

 In a few words, it may be said that centres of disruption 

 exist in the orders Orthoptera, Corrodentia, and Neuro- 

 ptera as defined by Brauer. Once a condition of equi- 

 librium is attained with respect to these three groups 

 we may be on the high road to something approaching 

 unanimity. 



Prof. Lefroy's book is essentially one on the orders 

 of insects. In the preface it is mentioned that the 

 book is based " upon the lectures given as the second 

 of three parts of a course occupying one year of a full 

 training in entomology." This apparently accounts 

 for the absence of any general chapters on structure, 

 biology, or development. On the whole, a very 

 reasonable compromise is made between the radical 

 tendencies of Handlirsch and undue conservatism, 

 and some 26 orders are separately treated more or less 

 in detail. The book is written for the student of 

 applied entomology, and its object is to teach him how 

 to recognise an insect in the field, to determine its sex, 

 to learn about its habits and the methods of control, 

 and to familiarise him with some of the more important 

 monographs or catalogues which provide references 

 to the literature. 



The conception of the book is a good one. In 

 carrying it out Prof. Lefroy assumes that the student 

 is working with a collection of specimens which he can 

 handle — illustrations are not very much believed in — 

 and has access to the " Zoological Record," " Genera 

 Insectorum" and the Review of Applied Entomology 

 for further information. References consequently do 

 not, as a rule, include the names of the journals con- 

 cerned, and sometimes only comprise the names of the 

 authors, along with the dates of their publications. 

 This method has very obvious difficulties, and, although 



2 A I 



