284 ANATOMY. 



wise sends off many branches to the muscles. A third, also cordiform 

 ganglion, lies closely to the posterior division of the second, and is 

 seated, as well as that, in front of the tridentiform process of the meta- 

 sternum ; from it, as well as from the posterior margin of the preceding 

 ganglion, fine radiating branches extend, all of which pass over the 

 sternal process into the abdomen, and proceed to its ventral plates ; 

 two central thicker ones, the cauda equina, proceed to the sexual 

 organs and the colon, distributing themselves there with many line 

 branches. The structure of the nervous system is similar in Dyticus 

 marginalis : the prothorax has its own ganglion, which, by means of 

 two thick and tolerably long nervous cords, is united to the cerebellum 

 (PI. XXXII. f. 2.). This ganglion lies always in front of the internal 

 sternal process, and runs with its posterior cords through both its 

 branches. The second ganglion, still larger than the first, lies pre- 

 cisely upon the mesosternum, in front of the commencement of its 

 internal process ; from it originate, as well as from the anterior, several 

 nerves among which we distinguish at the first ganglion two large ones 

 for the anterior legs (a, a), and at the second four thicker ones for the 

 posterior legs (b, b. and c, c.). The nervous cord rises from this 

 ganglion, runs between the branches of the sternal process, and lies 

 here between the coxae as a short nervous cord with four ganglia, which 

 somewhat increase in size, whereas the first is scarcely one quarter so 

 large as the second thoracic ganglion. From the circumference of 

 these four ganglia numerous nerves originate, particularly from the 

 last, which, radiating, proceed to the apex of the abdomen, and espe- 

 cially distribute themselves about the sexual organs. These last four 

 ganglia consequently belong, as well as the third in Melolontha, to the 

 abdomen, but they, however, rise as high as the coxae, for here the 

 most important muscles are found, whereas in the abdomen but few 

 large ones are to be met with ; on which account also in both cases the 

 ganglia are wholly wanting in the abdomen. 



This is not the case in the Lepidopiera and Hymenoptera, which 

 likewise have but two ganglia in the thorax, but in them the abdomen 

 also exhibits ganglia, namely, five in both orders, of which, however, 

 the two last are also very approximate ; and indeed in some cases, for 

 example in Pkilantkus piclus, they are grown into one, so that in it 

 we can detect but four distinct ganglia. The decrease of the ganglia 

 in the thorax arises in the Lcpidoplcra from the growing together of 

 most approximate ones, which takes place by degrees during the pupa 



