Mr. J. O. Westwood on the Earwig. 159 



In a short note published, in the 19th Number of the Zoological 

 Journal, when speaking of the instability of the decapod annulose 

 theory proposed in the ' Horse Entomologicse', the thorax being 

 typically su^jposed to be composed of five and the abdomen of seven 

 segments, the wings being regarded as two pairs of modified legs, 

 I observed that the earwig was sufficient to disprove its correctness, 

 the abdomen of that insect being in fact composed of nine distinct seg- 

 ments, the last of which is furnished, in addition to the caudal pincers, 

 with an exserted anal apparatus ; the thirteen segments of which the 

 body of an annulose animal is typically composed being here fully 

 and nearly equally developed in the perfect state, a circumstance of 

 very rare occurrence, as some or one of the abdominal segments, 

 although fully developed in the larva, are generally lost in the per- 

 fect state. 



And in a second short communication in the 20th Number of the 

 same work I have stated that being anxious to ascertain the situa- 

 tion of the spiracles along the body of an insect in which all the 

 thirteen segments were thus fully developed in the perfect state, (in 

 the hopes of discovering a clue to the solution of the remarkable 

 question raised by French entomologists relative to the structure of 

 the hymenopterous thorax, the hinder part of which is regarded by 

 them as composed of the basal abdominal segment,) I had discovered 

 upon examining some more specimens, that although the abdomen 

 of the male was 9-jointed that of the female possessed only 7 seg- 

 ments ; adding that this circumstance was very worthy of investiga- 

 tion as a clue to the solution of the question respecting the loss of 

 the abdominal segments in those insects which have fewer than 9 

 joints in that part of the body. 



The occurrence therefore of the insects in considerable numbers 

 in the flowers of the dahlia and nasturtium (for they are very fond 

 of creeping during the daytime into the attenuated spur of the lat- 

 ter flower as far as they can penetrate, leaving the abdomen sticking 

 up in the midst of the pistil and stamens,) has aff'orded me an oppor- 

 tunity of making the requisite investigations for attaining an accu- 

 rate acquaintance with the various particulars. 



The abdomen of the female, as already stated, apparently consists 

 but of seven segments, of nearly equal size, above ; but when seen 

 from beneath there appear to be only six unless the insect throws 

 up its tail ; the 6th ventral plate being much produced and conceal- 



and BruUe {Hist. Nat. des Insecfes, vol. ix. p. 21.), who have noticed the differ- 

 ence in tlie number of abdominal segments, without ascertaining that this difference 

 was apparent and not real, as subsequently shown. 



