THE ORGANS OF GENERATION 181 



that in these bladders, as in the larger ones of the flies, the spiral fila- 

 ment has torn from the distension, and only the rudiments of it are 

 present in the darker places. These bladders accompany all the intes 

 tines, pass everywhere between the muscles, and are particularly accu- 

 mulated superficially beneath the integument. A precise description 

 is consequently impossible, from the manifold reticulation of the 

 branches, and a single glance at the masterly representation of it in 

 Straus will explain it better than any words unaccompanied by figures 

 could possibly do, we therefore refer to his anatomy of Melolontha. 



The vesicular distensions in the tracheae of the Libellulce are found 

 chiefly in the thorax, and in it they lie exteriorly, contiguous to and 

 between the muscles. They are generally pyriform, whereas those of 

 the Lamellicornia and Lepidoptera are perfectly oval ; the bags also 

 appear to me to be connected by tracheae and to form distinct lacings. 



Among the Lepidoptera we find the bladders chiefly in the male 

 Sphinges and Phalente, and are sometimes small and sometimes large, 

 as in Acherontia Atropos, Ochs. They are of a coarser structure than 

 those of the beetles, so that the presence of the spiral fibre is here 

 subject to no doubt. According to a figure in Sprengel the membrane 

 of the bladder has sometimes a cellular appearance, and this might then 

 be considered as an approximation to the structure in the Lamelli- 

 cornia. 



SECOND CHAPTER. 



OF THE ORGANS OF GENERATION. 



131. 



THE second chief system of the vegetative organs comprises the 

 sexual organs destined to the propagation of the species. Under this 

 name we understand both the vesicular and the tubular parts which lie 

 in the abdomen generally affixed at one end, which, in a variety of 

 forms and connections are united together in main stems, and open in 

 one evacuating duct at the end of the abdomen beneath the anus. This 

 last definition is subject to no exception in true insects, for what has 



* Commentar., PI. III. fig. 24. 



