NO. 1687. THE THORAX OF INSECTS— 8N0DGRA88. 521 



Verlioeff extends his view of the many-segmented structure of the 

 insect l)ody to tlie abdomen (lOtma, li)08c, 1!)04). Here he iinds, in 

 the region of the hrst seven ordinary segments, seven primary seg- 

 ments and seven secondary ones. Beyond these are two genital seg- 

 ments, then the segment carrying the cerci, and finally, in tlie loAvest 

 insects, traces of three more beyond the last — the pygidium, the 

 meta[)Vgi(linm. and the telson. The gonapophyses and the cerci are 

 carried by the fifteenth, sixteenth, and seventeenth primitive seg- 

 ments, which are the eighth, ninth, and tenth persisting segments. 

 Verlioeff thus makes out a total of twenty aVxlominal segments. Add 

 to these the ten thoracic segments, one microthoracic segment, and 

 nine head segments, and an insect assumes the dignity of a creature of 

 forty segments ! 



III. THE MirROTHORAX. 



Embryologists have shown that the sclerites of the neck, the second 

 maxilhr of the head, the hind part of the subcesophageal ganglion, 

 and the gular plate, when present, are all derived from one metamere. 

 They usually reckon this metamere as the last segment -of the head, 

 while anatomists call its cervical parts in the adult the microfhorax. 

 This term has become pretty well established and will be adopted in 

 the present paper, but not implying that it is a part of the true 

 thorax. On the other hand there is no reason for calling it a head 

 segment. In many of the loAver insects its appendages, the second 

 maxilla' or labium, are not attached to the head but are suspended 

 from the gular membrane and associated much more closeh' with 

 the microthoracic sclerites than with the head [Spodromantis^ 25, 

 Sin.). The fact that the microthoracic ganglion is fused with the 

 true head ganglia preceding it signifies nothing more than does the 

 fusion of the first abdominal ganglion with that of the metathorax. 

 It is only when the sternal plate becomes transferred to the ventral 

 surface of the head, as the gula, that the microthorax takes any part 

 in the actual formation of the head. 



Verhoeft' (1002) regards the segment of the maxillipeds or poison 

 claws in the Chilopoda as the equivalent of the microthorax in insects. 

 This. hoAvever, is denied by Silvestri (1002), who says that the 

 maxilliped segment of the Chilopoda is the prothorax of insects. 

 Verhoelf (1003b) then further shoAvs that in Scolopendra there are 

 four pairs of nerves going to this segment, of Avhich the second is the 

 largest and innervates the appendages. In Polyp.nlota striata., a 

 Mantid, he discovers the same four pairs of nerves arising from the 

 subo'sophageal ganglion back of the labial nerves and going to the 

 microthorax and salivary glands. Here, hoAvever, the second is the 

 Aveakest and obviously because there are, according to Verhoeff 's view, 

 no microthoracic appendages, the labium not being regarded as such. 



