16 



THK CLASS OF INSECTS. 



Fig. 19. 



gradually incurved toward the base (Fig. 18), and the three 

 pairs of rlmbdites approach each other so closely that the two 

 outer ones completely ensheath the inner, until a complete 

 extensible tube is formed, which is gradually withdrawn entiielv 

 within the body. 



The male genital organ is originally composed of three pairs 



(two pairs, apparently, in ^Ex- 



c/ma, Fig. 19) of tubercles all 



arising from the ninth abdominal 



ring, being sternal outgrowths 



and placed on each side of the 



mesial line of the body, two be- Fl ^ 20. 



ing anterior, and very unequal in size, and the 



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

 ternal genital organs are to be considered 

 as probably homologous with the limbs, as 

 Ganin has shown that they bud out in the 



same manner from (sec p. 704 

 ; 

 fig. 655) the arthromere.* 



" b This view will apply to the 

 genital armor of all Insects, so 

 far as we have been able to observe. It is 

 so in the pupa of ^Esclma (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 jEschna and 

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

 forin 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 deflning the ideal ring, or primary zoological 

 element of an articulated animal than the terms sunlit? or iuonitc, which seem too 

 vague; we also propose the term nrtliroili-rni for the outer crust, or body walls, of 

 Articulates, and t/rtliroji/c/ira for the pleural, or limb-bearing region, of the body, 

 being that portion of the arthromere situated between the tergite and sternite. 



FK;. 111. The rudiments of the male intromittent organ of the pupa of .Kschna, 

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

 large and rounded inclosing the smaller linear oval pair. 



FlG. 20. The same in the Humble-bee, but consisting of three pairsof tubercle-, 

 x, y, Zj 8,9, 10, the last three segments of the abdomen. 



FlG. 21. The rudimentary ovipositor of the pupa of .Km-him, a Dragon-fly. 



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

 of the eleventh abdominal ring ara seen, d, the ba.-e of one of the abdominal f.-tl-e 

 gills. The ovipositor of Cicada is formed in the same way. Figs, \\-2~i original. 



Fig. 21. 



Fig. 22. 



