1891.] ENTOMOLOGICAL NEWS. 9 



abdominal segment. These are represented in the correspond- 

 ing images, in which state they much resemble antennae; they 

 are called anal forceps, cerci, or caudal setts. Male insects have 

 sometimes one or two pairs of jointless claspers at the apex of the 

 abdomen. Female insects may have the abdomen furnished with 

 a sawing, piercing, or boring organ the ovipositor, by which the 

 eggs are implanted into various substances. A sting is an ovi- 

 positor modified to form an organ of defence; it exists in females 

 only, of some insects. Cornicles, nectaries, siphnncles, or honey 

 tubes, are small tubes, two in number, found on the abdomen of 

 plant-lice and certain other insects, through which a liquid 

 (" honey-dew" ) is secreted. 



With this we complete our sketch of the external anatomy of 

 insects. Their internal anatomy is hardly an elementary study, 

 owing to its difficulty, but from its importance it cannot be over- 

 looked here. 



If a cross-section were made of the body of a cat, or other 

 back-boned animal, the relative positions of the main nerve 

 (spinal) cord, the main blood vessel (aorta) and the alimentary 

 canal would be seen to be as follows. The most dorsal of the 

 three would be the nerve cord; below it, that is, on its ventral 

 side, would be the main blood vessel; below the latter would be 

 the alimentary canal, the most ventral of the three. These po- 

 sitions would, of course, be equally true for the human species. 



But the relative positions of these three great organs in Ar- 

 thropods (and consequently in insects) is different. Here the 

 main blood vessel is the most dorsal, below it is the alimentary 

 canal, below the latter is the nerve cord, which is here the most 

 ventral of the three. 



The body wall of an insect is made up of three (microscopic) 

 layers, - 



1. An outer chitinous layer, or acticle. 



2. A median cellular layer, or hypodcrinis. 



3. An inner layer, or basal membrane. 



The alimentary canal has its beginning at the mouth opening 

 and extends as a more or less convoluted tube, divided into va- 

 rious parts, through the length of the body, to its external open- 

 ing (amis) in the apex of the abdomen. The principal parts of 

 the canal are the pharynx, situated within the head, connected 



