The Microscope and Biology. By W. Wesche". 403 



inquiry by a separate study of the parts. They may be divided 

 thus : — 



I. — General Structure. This includes, in addition to the 

 insect as a whole, (a) the limbs ; (b) the finer bristles ; (c) the sense- 

 organs. 



II. — The Armature of the Mouth. 



III. — The Contents of the Abdomen : (a) food ; (b) structure. 

 IV. — The Genitalia. 



I. — General Structure. 



This may be regarded from several points of view, as it is 

 (a) Utilitarian ; (b) Sensorial ; (c) Eaptorial ; (d) Secondary sexual. 



A. Utilitarian. — A study of the wings and their nervation 

 affords information as to the character of the flight, but also is in 

 a measure a guide that will tell something of the evolution of the 

 species. The openings of the tracheae on the thorax and the 

 abdomen show us how sounds are made, and how the insect oxy- 

 genates the blood. The immense importance of keeping the antennae 

 clean is shown by the contrivances on the fore limbs, such as the 

 brush on the metatarsi of the Muscidae, or the comb on the tibiae 

 of the Hymenoptera. The Microscope will show how it is possible 

 for an insect to skate on the surface of smooth water, and para- 

 sitism can be recognised by the flattened form of the body and 

 the character of the legs, particularly the claws. 



b. Sensorial. — This section requires almost exclusively high- 

 power work, and will in some cases necessitate the cutting of 

 sections. All or most of the many modifications, such as " taste 

 hairs," or " olfactory pits," and other structures so clearly brought 

 before us in " Senses of Animals," * can be seen on preparations 

 mounted with pressure : they must be looked for on the antennae 

 and mouth-parts.f On the legs will be found some sense-organs, 

 particularly in Diptera, which are comparatively rare, and which 

 I have described in a former paper : those on the coxae are more 

 frequently met with than the organs on the tibiae.f 



C Raptorial. — Under this heading I include all modifications 

 that are used in holding prey. The most usual characteristic is 

 an enlargement of the femur to contain the much-developed 

 muscles, and the legs and often the fore coxae have rows of strong 

 sharp spines. But strong spines are equally characteristic, and 

 the arrangement is apt to alter in different families. This type 

 is usually easily recognisable, as it is found in both of the sexes, 

 but there are a number of genera in the Syrphidae which, from the 



* Senses of Animals, 1889, Sir John Lubbock. 



t Sopra certi organi di senso nelle antenne dei Ditteri. Dr. Paul Mayer, 

 Reale Accademia dei Lincei, 1878-79. 



t Some New Sense Organs in Diptera. Journ. Quekett Micr. Club, 190-i. 



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