16 



THE CLASS OF INSECTS. 



gi-aclually incurved toward the base (Fig. 18), and tlie thi-ee 

 paii-s of rhabdites approach eacli other so closely that the two 

 outer ones completely ensheath the inner, until a complete 

 extensible tube is formed, which is gradually withdrawn entirely 

 within the body. 



The male genital organ is originally composed of three pairs 

 (two i^airs, apparently, in u^s- 

 .„ cima, Fig. 19) of tubercles all 

 arising from the ninth abdominal 

 ring, being sternal outgrowths 

 and placed on each side of the 

 /—rry~\ mesial line of the body, two be- rig. 20. 



vJsLL^ ing anterior, and very unequal in size, and the 

 Fig. 19. third pair nearer the base of the abdomen. The ex- 

 ternal genital organs cannot be considered as 

 in any way homologous with the limbs, which 

 are articulated outgrowths budding out be- 



)_ a 



- II) 



tween the sternal and pleural r 



pieces of the artliromere.* 

 '^ This view will apply to the 

 Fig. 21. genital armor of all Insects, so 

 far as we have been able to observe. It is 

 so in the pupa of u^schna (Fig. 21), and 

 the pupa of Agrion (Fig. 22), which com- 

 pletely repeats, in its essential features, the 

 structure of the ovipositor of Bombus. Thus in uS^sclina and 

 Agrion the ovipositor consists of a pair of closely appressed ensi- 

 form processes which grow out from under the posterior edge of 

 the eighth abdominal ring, and are embraced between two pairs 



* This term is proposed as better defining the ideal ring, or primary zoological 

 element of an articulated animal tlian the terms somite or zoonite, -whicli seem too 

 vague; we also propose the term arthroderm for the outer crust, or body walls, of 

 Articulates, and arthropleura for the pleural, or limb-bearing region, of the body, 

 being that portion of the arthromei-e situated between the tergite and sternite. 



Fig. 19. The rudiments of the male intromittent organ of the pupa of ^Eschna, 

 consisting of two flattened tubercles situated on the ninth ring; the outer pair 

 large and rounded inclosing the smaller linear oval pair. 



Fig. 20. The same in the Humble-bee, but consisting of three pairs of tubercles, 

 a^i 2/. «! 8) 9> 10, the last three segments of the abdomen. 



Fig. 21. The rudimentary ovipositor of the pupa of ^■Eschna, a Dragon-fly. 



Fig. 22. The same in pupa of Agrion, a small Dragon-fly. Here the rudiments 

 of the eleventh abdominal ring is seen, d, the base of one of the abdominal false 

 gUls. — Figs. 14-22 original. 



