( cxxi ) 



its falces often articulated to it, this is the main dorsal part 

 of the armature ; in addition to this there is the cingula or 

 girdle, which really encircles the whole abdomen and is repre- 

 sented in the sternite also ; this is the hindermost portion of 

 the genitalia, the saccus forming in reality a portion of it ; 

 the cingula is sometimes a mere ring of fine chitin, more often 

 it is considerably developed, and is fused in the tergite with 

 the back part of the tegumen ; in some cases the cingula is 

 articulated at the meeting-place of the tergite and sternite. 

 The anus is emitted directly below the tegumen. In the 

 sternite the largest organs are the harpagones or clasps, these 

 being paired; the ringwall of Zander is a chitinous collar 

 connected with the harpagones through which the sedoeagus 

 passes ; the furca, whilst not really homologous with the ring- 

 wall, yet seems to take its place in most of the Rhopalocera 

 and in some other cases. The sedceagus only needs mention 

 to explain that it represents the whole organ, and that the 

 penis, the vesica and the ductus ejaculatorius are parts of it. 



In the Trichoptera the superior appendages are, I believe, 

 homologues to a large extent of the tegumen and the inferior 

 appendages of the harpagones. In the Diptera the same 

 applies to a certain extent, but owing possibly to the position 

 assumed by these organs in this order they are reversed by 

 some authors. The Coleoptera have not, so far as I can trace, 

 true homologues to the Lepidopterous external organs ; 

 neither, I believe, have the Hymenoptera, at least so far as 

 the Aculeata go, though they are provided with intricate 

 armature. The Odonata are quite distinct in all their char- 

 acters. 



It will probably be well to consider the more lowly orders 

 first and to work upwards. 



I have only been able to examine two species of the Thy- 

 sanura, which group have no clasping organs, but merely 

 sensory apophyses ; this also is true with the CoUembola, and, 

 I believe, the Thysanoptera. 



Petrobius maritimus, Leach, 



has an enveloping outer case surrounding the sedoeagus, 

 which (case) is slit lengthwise along the dorsum and the 



