HALF-HOURS AT THE MICROSCOPE. 379 



of the A7iopliira, for which he had collected the material. These 

 are now, I believe, at the British Museum, and may be studied by 

 those who will take the needful steps to procure access to them. 



Fly (PI. XXIII., Fig. 4). — The form of the antennae; the vena- 

 tion of the wings, in so far as can be made out ; the general 

 aspect of the legs and their appendages (hooks, flaps, etc.), all 

 proclaim this to be a species of Scatophaga. It furnishes a good 

 opportunity for saying a few words on the parts composing the 

 body of an insect. There are, then (with comparatively few 

 exceptions), thirteen segments in all insects. These may be thus 

 enumerated : — 



I. — Head (composed of 5 sub-segments). 



2, 3, 4. — Thorax. 



5 — 13. — Abdomen; the first six segments containing the 

 organs specially devoted to the reception and digestion of food ; 

 the remainder modified in various ways in connection with the 

 genital organs. Two segments only of the thorax have spiracles, 

 the first and the last. The former of these is what is sold by 

 object-vendors for " Spiracle of Fly," and is the one commonly 

 figured. It is curious to find that the male fly has one pair of 

 spiracles more thnn the female, indicating greater development of 

 the respiratory function for flight in search of her. A correlated 

 fact is that the compound eyes with him occupy a much greater 

 extent of surface, in some instances all but covering the crown of 

 the head. The peculiar hooks terminating the abdomen of the 

 male Scatophaga are here well shown. 



The males of some flies feed upon pollen and nectar, whilst 

 their partners prefer gross decaying substances. 



Hairs of Tiger-Moth Caterpillar (PI. XXIII., Fig. 5).— The 

 introduction of this specimen to our boxes must be regarded as 

 an important fact, for the necessity of making ourselves thoroughly 

 acquainted with the structure of the common objects around us 

 comes to my mind with continually increasing force. 



The caterpillars of the Bombycidce (to one of which those 

 before us belong), many of them possess hairs capable of pro- 

 ducing urtication to a greater or less degree. It is not yet quite 

 settled to what this is due. Those, however, who are in the habit 



