31 



parts around, and frequently membranous in structure, are called 

 fenestrae. In the males of some species they are replaced by ocelli. 



On glancing at the ventral surface we are at once confronted with 

 two other striking points in cockroach anatomy — the enormous 

 development of the coxae of all the legs, and the spiny armament of 

 the tibiae. 



In recent cockroaches the elytra and wings differ considerably in 

 both shape and texture. Amongst the various species, too, there is 

 much diversit}' in their length compared with that of the abdomen, 

 being longer in some, abbreviated in others, while from some species 

 they are absent altogether. In some cases the wings are less fully 

 developed than the elytra, while the length of these appendages may 

 be different in the two sexes. It might seem that here we have a 

 ready means of grouping the various genera and species, but in 

 practice it is found that the relative development of the alar organs 

 is of slight nnportance, as indeed is the case throughout the 

 Orthoptera. 



Of the elytra the principal nervures, omitting the costa, are four 

 in number, being named in order from the costal margin : — 



(a) the mediastinal ; 



{b) the radial or scapular ; 



(c) the median or ulnar (which sometimes is in duplicate, the 



two being called the anterior and posterior medians) ; 

 {(I) the dividing nervure. 

 Tiie areas thus formed are : — 

 («) the mediastinal, above the nervure of the same name ; 



(b) the radial or scapular ; 

 {c) the median ; 



{(I) the anal or axillary. 



Being very variable and sometimes abbreviated, the median 

 nervure is looked upon as unimportant, and consequently the 

 whole of the area between the radial and dividing nervures is called 

 the median. In the wing the prmcipal nervures hold the same 

 relative positions ; but between the radial and the ulnar there is 

 sometimes a prominent nervure called the " spurious " ; the anal 

 area, moreover, which at rest is folded longitudinally like a fan, 

 often occupies more than haU' the wing and is much more delicate 

 in structure than the anterior part, which in texture resembles to a 

 great extent the elytron. Wings and elytra are both well filled 

 with branches of the several nervures. It should be noticed that 

 when the alar organs are folded there is no mid-dorsal suture, but 

 the left elytron overlaps tbe light. 



In each sex there appear to be ten abdominal segments, besides a 

 couple of " podical plates " lying one on each side of the anus, 

 which, according to Huxley, may represent the dorsal part of an 

 eleventh. The first segment is rudimentary, especially the ventral 

 plate. In the female the 8th and 9th segments are visible only 

 when the abdomen is distended. In the same sex the ventral plate 



