358 NATURAL HISTORY. 



of some of the stigmata, caused by the violent expulsion of the air from the tracheal system. 

 With regard to this second set of sounds, however, a French observer, M. Perey, comes to a different- 

 conclusion, and declares that the removal of the above-mentioned scaly parts, or even the absolute 

 stopping of the stigmata, does not prevent the buzzing, which he believes to proceed from the 

 friction of the bases of the wings upon the solid parts surrounding them. 



The Hymenoptera are for the most part of small or moderate size, few species exceeding 

 two inches in length, or three in expanse of wings. A great number, especially of the parasitic 

 forms, are exceedingly minute. They appear to be very generally diffused over the surface of the 

 earth, but are probably more numerous in the warmer regions than in temperate zones. The 

 number of described species is estimated at about 16,000, but this must bear only a very small 

 proportion to the total Hymenopterous population of the globe. It has been estimated that we 

 have about 3,000 species in Britain, and, making every allowance for the probable exaggeration 

 of this estimate, owing to comparative want of thorough knowledge, we may believe that the 

 number of species of Hymenoptera does not fall very far short of that of the Beetles in the 

 British area ; and, extending the argument to a wider field, it may be assumed that the Hymenoptera 

 of the whole world are not much less numerous than the Beetles. 



Geologically the Hymenoptera are not very ancient. Professor Heer has described a fragment 

 of a wing from the Lias of Schambelen, in Switzerland, as possibly belonging to a species of Ant ; 

 but he is very doubtful whether it represents a Hymenopterous insect at all, and an inspection of his 

 figure will show that his doubts are veiy well founded. Several species have been described as 

 occurring in the Lithographic limestone of Solenhofen, in Bavaria, which belongs to the Upper 

 Oolite ; but these are regarded as doubtful by good authorities, and it is not until we reach the 

 Tertiaries that unmistakable remains of Hymenopterous insects are met with. Here, however, 

 they occur in all the deposits in which fossil insects are found, and are generally so nearly allied to 

 existing types that they may safely be referred to the same families, and often to the same genera. 



The classification of the Hymenoptera has undergone some superficial changes, although the 

 views of entomologists as to the relations of the families have generally remained much the same. 

 Latreille divided them into Aculeate and Terebrant Hymenoptera, according as the females were 

 provided with stings or ovipositors, and the second group into Pupivora, with the abdomen attached 

 to the thorax by a narrow part, and Securifera, in which the union of these two parts of the body 

 is by the whole width of their bases. This arrangement was very generally followed for many years, 

 and it seemed to be confirmed by the observation that throughout the whole of the Terebrantia of 

 Latreille the trochanter consists of two rings, whilst in the Aculeata there is only one. The 

 differences between the two great divisions of the Terebrantia ai-e, however, so great and important, 

 and the resemblances of the second of them to the Aculeata are so striking, that of late several 

 leading authorities have adopted a triple division of the order, in which all the broad peculiarities of 

 the insects are duly taken into consideration. This arrangement we shall adopt here, as it seems 

 to enable all the affinities of the different families to be shown most distinctly. The three great 

 tribes, or sub-orders, thus arrived at are as follows : 



I. ACULEATA : having the trochanters simple ; the abdomen attached to the thorax by a narrow 

 part ; the females provided with a retractile sting connected with a poison-gland ; and the antennae 

 with twelve joints in the females and thirteen in the males. The larvae are footless grubs, with no 

 posterior aperture to the intestine. 



II. ENTOMOPHA^A : having the trochanters composed of two rings ; the abdomen as in the 

 preceding ; the females provided with an ovipositor, which usually projects from the body, and is 

 enclosed by a sheath formed by two valves ; and the antennae with a variable and often very large 

 number of joints. The larvae are like those of the preceding group. 



III. PHYTOPHAGA : the trochanters of two rings ; the abdomen attached to the thorax by the 

 whole width of its base ; the ovipositor either a saw-like organ consisting of two valves, or an 

 ovipositor nearly agreeing in structure with that of the preceding group ; antennae generally with a 

 moderate number of joints. The larvae are vegetable feeders, usually resembling Caterpillars, having 

 six more or less developed thoracic legs, and generally a number of pro-legs on the abdominal 

 segments ; their alimentary canal has an anal orifice. 



