84 Mr. A. S. Packard on the Development 



lying on each side of the labrum with its palpi and the maxillae. 

 These appendages do not as yet project much beyond the an- 

 tennae, being short and papilliform, preserving the general form 

 of the same organs in the larvae. 



At this period the elements [sterno-rhabdites, Lacaze-Duthiers) 

 composing the ovipositor lie in separate pairs, in two gi'oups, 

 exposed distinctly to view. The ovipositor thus consists of three 

 pairs of slender non-articulated tubercles arising on each side of 

 the mesial line of the body, in juxtaposition. The first two pairs 

 arise from the eighth abdominal ring, and the third pair grow 

 out from the anterior edge of the ninth ring. The ends of the 

 first pair scarcely reach beyond the base of the third pair. With 

 the growth of the semipupa the terminal or tenth ring decreases 

 in size, the tip of the abdomen is gradually incurved towards 

 the base (fig. 2), and the three pairs of rhabdites approach each 

 other so closely that the two outer ones completely ensheath 

 the inner, until a complete distensible tube is formed, which 

 gradually is withdrawn entirely within the body (see fig. 4). The 

 male genital organ is originally composed of three pairs of non- 

 articulated tubercles, all arising from the ninth abdominal ring, 

 being sternal outgrowths, and placed on each side of the mesial 

 line of the body, two being anterior and very unequal in size, 

 and the third pair nearer the base of the abdomen. Thus, in 

 their position, the three pairs of tubercles destined to form the 

 male intromittent organ cannot be said to be strictly homological 

 with the female ovipositor; nor can the external genital organs 

 be considered in any way homologous with the limbs, which 

 are articulated outgrowths budding out between the sternal and 

 pleural pieces of the arthromere*. This view will apply to the 

 genital armature of all insects, so far as I have been able to ob- 

 serve. It is so in the larva of Agrion, which completely repeats 

 the structure of the ovipositor oi Bombus in its essential features 

 detailed above. Thus in Agrion the ovipositor consists of a pair 

 of closely appressed ensiform processes which come out from 

 under the posterior edge of the eighth abdominal ring, and are 

 embraced between two pairs of thin lamelliform pieces of similar 

 form and structure, arising from the sternite of the ninth ring. 

 These sternal outgrowths do not homologize with the long, fili- 

 form, antenna-like, jointed appendages of the tenth ring, as 

 seen in the Perlidae and most Neuroptera and Orthoptera, which, 



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

 zoological element of an articulate animal than the terms somite or zoonite, 

 which seem too vague ; so also 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 arthromere comprised between 

 the tergite and sternite. 



