88 



INSECTS 



CHAP. 



It is no reproach to morphologists that they have not yet 

 agreed as to the number of segments that may be taken as 

 typical for an Insect, for all the branches of evidence bearing on 

 the point are still imperfect. It may be well, therefore, to state 

 the most extreme views that appear to be at all admissible. 

 Hagen^has recently stated the opinion that each thoracic segment 

 consists really of three segments an anterior or wing-bearer, a 

 middle or leg-bearer, and a posterior or stigma-bearer. There 

 seems to be no reason for treating the stigma as being at all of 



Fig. 47 Diagram of exterior of insect : the two vertical dotted lines indicate the 

 divisions between H, head; T, thorax; and A, abdomen: a, antenna; h, labrum ; 

 c, mandible ; d, maxillary palpus ; e, labial palpus ; /, facetted eye ; g, pronotum ; 

 h, mesonotum ; i, metanotum ; k, wings ; Zj to Zj^, abdominal segments ; m, the 

 internal membranous portions uniting the apparently separated segments ; n, cerci ; 

 0, stigma ; p, abdominal pleuron bearing small stigmata ; q-^^ q^, qs, pro-, meso-, 

 meta-sterna ; r^, mesothoracic episternum ; si, epimeron, these two forming the 

 mesopleuron ; r.,, s^, metathoracic episternum and epimeron ; t, coxa ; v, trochanter ; 

 w, femur ; x, tibia ; y, tarsus ; z, gula. 



the nature of an appendage, and the theory of a triple origin for 

 these segments may be dismissed. There are, however, several facts 

 that indicate a duplicity in these somites, among which we may 

 specially mention the remarkable constancy of two pleural pieces 

 on each side of each thoracic segment. The hypothesis of these 

 rings being each the representative of two segments cannot there- 

 fore be at present considered entirely untenable, and in that case 

 the maximum and minimum numbers that can be suggested 

 appear to be twenty-four and eleven, distributed as follows : 



^ Stettin. Ent. Zeit. 1. 1889, p. 165. 



