INTRODUCTION. xiii 



" The type of veins in the Micropterygina differs from that described above in 

 two essential particulars, viz. : (1) there may be three additional veins in the fore-wings, 

 rising out of vein 11 or 12 ; and (2) the veins of the hind-wings are practically identical 

 in number and structure with those of the fore-wings, being thus much more numerous 

 than in the ordinary type. There is also often a system of cross-bars between the veins 

 near the base of the wing (Plate I., figs. 22 and 23, neuration of Hepialus). 



"The structure of the veins can be best observed on the under surface of the wing, 

 where they are more prominent. The student should begin by completely denuding of 

 scales a few wings of common species : the wing should be cut off and laid on a moistened 

 piece of glass, to which it will adhere ; the scales should then be removed, first from one 

 surface and then from the other, with a, fine, moist camel's-hair brush — an operation 

 requiring a little patience and delicacy of touch ; the veins will thus be rendered con- 

 spicuous.* When, however, the student has familiarised himself with the general subject, it 

 will not be found necessary in practice to resort to this process ; most details will be easily 

 observed without denudation t ; where this is not the case (as where the veins are closely 

 crowded or otherwise obscured), the scales can be removed with the brush on the under 

 surface in the locality of the difficulty only, without cutting off the wing or otherwise 

 damaging the specimen, which remains in the collection available for all purposes as 

 before ; with proper practice, even the smallest species are amenable to this treatment, 

 which does not require more skill than the actual setting of the specimen. Some workers 

 prefer to put a drop of benzine on the spot, which renders it temporarily transparent ; the 

 effect is short-lived, as the benzine evaporates rapidly, and the cilia (if long) are liable to 

 be damaged by this method." 



The Legs consist of the following joints (see Plate 1., tig. 21) : (1) coxa, (2) trochanter, 

 (3) femur, (4) tibia, (5) tarsus, (li) claw. The tarsus normally consists of five joints, 

 but is more or less aborted when the leg is not employed for walking. The spines 

 (SS) on the tibiae of the several legs vary considerably in size and number. They 

 are often useful to the systematist for purposes of classification. 



THE ABDOMEN 



consists of nine segments, some of which are often fused together. It contains the 

 various internal organs, of which the most important are those of Digestion and 

 Reproduction. The Digestive Hystem (Plate I., fig. 10) consists of the following organs: 

 A, the cesophagtts, or throat; C, the sucking stomach; 1), the ventriculus or stomach ; 

 E,the small intestine; G, the ccecum ; H, the colon ; K, the biliary vessels; N, the salivary 

 vessels. The function of the sucking stomach is to exhaust the air in the throat and 

 proboscis, and thus to cause the ascent of the fluids into the stomach when the insect is 

 feeding. 



III.— ORIGIN OF SPECIES. 



The theory of the origin of species as propounded by Darwin may be thus very 

 briefly summarised : — 



* For the examination of the wings taken from dried specimens. I have found that immersion in methylated spirits 

 renders the veins visible after partial denudation with the camel's hair brush. With recent specimens, however, the 

 scales can easily be entirely removed. 



f I have found considerable difficulty and uncertainty in examining the neuration of undenuded specimens. 



