» Common Cockroach. 201 



inferiorly by the insertion of the Malpighian tubules in a 

 circle around the digestive canal. 



j. Malpig-hian tubules, in number from twenty-four to thirty; 

 and by their insertion in a zone around the lower end of 

 the chylific stomach, marking- the commencement of the 

 short segment which may be spoken of as the small in- 

 testine. 



Jc. Small intestine. 



I. Large intestine or colon ; found ordinarily to be in its upper 

 part distended with the refuse of the ingesta, and to be 

 below of smaller calibre, and corrugated so as to present a 

 beaded appearance. 



m. Rectum divided into longitudinal areae by muscular bands, 

 which alternate with internally placed lamelliform produc- 

 tions of the intestinal walls. The ridges thus developed 

 upon the rectum receive in the larvae of certain of the 

 Libellulidae a very rich supply of tracheae, and, together 

 with a valvular apparatus developed from the caudal tegu- 

 mentary skeleton, constitute their aerating organ. 



n. First abdominal ganglion, closely approximated to the third 

 thoracic, and placed at a little greater distance from the 

 second abdominal ganglion posteriorly. The sixth abdo- 

 minal ganglion should have been drawn as somewhat heart- 

 shaped, but laterally constricted so as to have the appearance 

 of being made up, as the history of its development, of its 

 comparative anatomy, and of the distribution of its nerves 

 shows it to be, of two distinct ganglia. The two oviducts 

 pass to their point of fusion from the outside of the angle 

 bounded by the nerves, seen to pass off from this ganglion ; 

 the receptacula seminis, which are small, and not given in 

 this figure, are situated within that angle and at its apex ; 

 distally to them, but within the angle, the two ducts of the 

 numerous colleterial glands pass to the orifice within which 

 they open on the sternum of the tenth segment. The first 

 sub-oesophageal ganglion is not seen in this figure, being, as 

 always in insects, in such close apposition to the supra-oeso- 

 phageal or cercbroid ganglia, as to have been sometimes, 

 but inconveniently, described, as together with them making 

 up a ' brain.' Counting however this ganglion whence the 



