THE VENTRAL COUD. 28:> 



state. Thus, from the first and second ganglia of the caterpillar the 

 ganglion of the prothorax originates, from the third and fourth the 

 common very large ganglion for the connate meso- and metathorax ; the 

 fifth ganglion of the caterpillar,, as well as the sixth, entirely disappear; 

 the seventh to the eleventh are found likewise in the imago. The 

 ganglion of the prothorax lies in both orders between the branches of 

 the internal sternal process, and gives off, besides the thick nerve for 

 the anterior legs, finer branches for the muscles ; the ganglion of the 

 ineso- and metathorax lies upon the central surface of the sternum, it 

 is very large, and somewhat long; many nerves spring from it, eight 

 of which are particularly distinguished. Two and two form an equal 

 pair ; the first and third pairs go to the wings, the second and fourth 

 to the feet, the remaining finer ones distribute themselves among the 

 muscles ; the last pair, lying closely to the connecting cord, passes with 

 this into the abdomen, and distributes itself in its first segment by 

 means of several filaments. In Bombus muscorum, according to Tre- 

 viranus' figure *, the second thoracic ganglion consists of an anterior 

 larger and a posterior smaller half ; but in many of the Hymenoplera 

 inspected by me, for example, in Vespa Germanica, I could not dis- 

 tinguish them, there was but a single large ganglion visible. 



Lastly, there are insects in which but one ganglion is found in the 

 thorax, these are the Diptera. In them it is known that the thorax 

 is formed of but one undivided piece, which consists especially of the 

 mesothorax, to which the very small pro- and metathorax are but 

 appended. In the mesothorax also we find the chief muscles, namely, 

 the large direct dorsal and alary muscles, and accordingly a single 

 large ganglion, which lies upon the centre of the sternum, between the 

 intermediate and posterior legs. It takes the form of a long ganglion 



A o o o o 



(PI. XXXII. f. 4.), from which spring six main nerves for the legs. 

 I have not yet detected nerves for the wings proceeding directly from 

 the ganglion ; perhaps they may be branches of the nerves of the feet. 

 From the posterior margin of the ganglion a simple strong nervous 

 filament passes, which, running between the apertures of the coxae, 

 proceed into the abdomen ; closely before its entrance it gives off on 

 each side a fine nerve, but in the abdomen itself it has no branch as 

 far as the middle of its course. Here it first distends into a small 

 ganglion, from which on each side a fine furcate nerve originates. A 



Biologic, vol. v. PI. I. II. and III. 



