AN INTRODUCTION TO ENTOMOLOGY. 



lights; and it is not an uncommon occurrence in summer-time to see 

 hundreds of them flying about a single street-lamp. 



They are very fragile insects, 

 with large delicate fore wings, 

 with the hind wings much smaller 

 or wanting, and with the abdo- 

 men furnished at its caudal end 

 with either two or three many- 

 jointed, thread-like appendages 

 (Figs. 64 and 640). 



The body is smooth, not 



FIG. 64. May-fly. 



FIG. 640. Canis. 



clothed with scales or hairs. The head is free, with atrophied 

 mouth-parts, and inconspicuous antennae. These are composed 

 of two short stout segments succeeded by a slender many-jointed 

 bristle. The thorax is robust, with the mesothorax predomi- 

 nant. The great development of this segment is correlated 

 with the large size of the fore wings. The abdomen is long, 

 soft, and composed of ten segments. In the male there is a pair 

 of clasping organs placed ventrally at the extremity of the ninth seg- 

 ment ; these are usually two-, three-, or four-jointed, and are termed 

 the forceps-limbs. Just behind the forceps-limbs are the paired ex- 

 ternal sexual organs. The form of the external parts of the repro- 

 ductive organs is remarkable ; each vas deferens and each oviduct 

 has a separate opening. In the male these openings are between the 

 ninth and tenth abdominal segments, as indicated above ; in the fe- 

 male, between the seventh and eighth. 



The May-flies have received considerable attention in popular 

 writings on account of their ephemeral existence in the adult state. 

 All have read of the insects that live but a day. Reference is made 

 in these accounts to members of this family ; and although the popu- 

 lar idea is fallacious, it has some foundation in fact. Strictly speak- 

 ing, the May-flies are long-lived insects ; some species appear twice 

 annually, once in the spring, and again in the autumn ; but as a rule 

 one, two, or even three years are required for the development of a 



