23 



THE POPULAR SCIENCE MONTHLY. 



edge is indented like a bean, or like the kidneys of vertebrates. 

 The eyes are then said to be reniform. 



The organ of vision is sometimes made more complete by sim- 

 ple eyes, detached from the general group and permitting the 

 insect to distinguish parts of space outside the field of the faceted 



eyes. These supplementary organs, 

 called ocelli, usually three in num- 

 ber, are arranged triangularly be- 

 tween the reticulated eyes. 



The antennae are articulated ap- 

 pendages which insects bear on the 

 head, near the eyes, sometimes for- 

 ward of them, sometimes behind 

 them, and which are often greatly 

 developed. 



The antennae are generally re- 

 garded as organs of touch ; there is 



go, ganglion of the optic nerve ; no, 

 optic nerve. (According to Nuhn.) 



Fig. 11. Section of an Insect's Eye. 

 C, cornea ; fac, cones ; hr, rods ; P, 

 pigmentary sheathings of the rods; h ar dly any doubt about the fact. 



Some naturalists make them the 

 seat of the smell ; others consider 

 them connected with hearing ; and some locate both senses in 

 them. However it may be, they are formed of a series of articu- 

 lations united to one another, the number and form of which fur- 

 nish entomologists with good characteristics for classification. 



The antennae are straight or bent. The basilar joint, which 

 is in direct relation with the head, is called the scape ; in bent 

 antennae it is usually very large, and forms an obtuse angle with 

 the next joint. The club, or terminal part of the antenna, is 

 sometimes in the shape of an olive, and is composed of a variable 

 number of joints. The whole number of joints between the scape 

 and the club constitutes the funicle. Characteristic forms of an- 

 tennae are represented in Fig. 12. 



The thorax comprises three rings more or less closely joined : 

 the prothorax, mesothorax, and metathorax. The prothorax bears 

 the first pair of legs ; it is largely developed in the Coleoptera and 

 Hemiptera, in which it appears as a horny buckler, and is freely 

 articulated with the mesothorax. It is the corselet of the old au- 

 thors, and is called the pronotum by the entomologists of to-day. 



The mesothorax bears the second pair of legs and the first pair 

 of wings, which are sometimes horny ; we perceive on the upper 

 part of the insect only a small triangular portion of it, which is 

 hardly visible in some species, and is called the scutettum or 

 escutcheon. All the rest of the dorsal part is covered by the 

 wings. 



The metathorax is closely united to the preceding ring, and 

 frequently also to the first rings of the abdomen. It bears the 



