INSECTA. 



949 



form of cord and distribution of ganglia exists 

 even in many of the more perfect Coleoptera, 

 as in the Carabidic (fig. 407) and Hydrophi- 



Fig. 407. 



Nervous system of Carabus monills. 



lidie. Swammerdam long ago showed this 

 aggregation of nervous matter in the maggot of 

 the cheese-hopper, and Burmeister has since 

 observed even a more concentrated form in the 

 larva of Eristalis tenax, the rat-tailed maggot 



of cesspools and privies. In the latter instance, 

 as seen also by ourselves, the nervous system 

 consists of a short nodulated cord, which does 

 not extend beyond the three very short thoracic 

 segments, and the greater portion of the body, 

 the nine posterior segments, receives its nerves 

 directly from the cord in the thorax, and not 

 from a ganglion in each segment. This is a 

 circumstance the more remarkable, if, as be- 

 lieved by Straus and others, the existence of 

 the ganglia is regulated entirely by the mobility 

 of the segments or the existence of appendages, 

 because, in these instances, the extremities of 

 those segments in which the cord is placed 

 are undeveloped, or only, as in Eristalis, in 

 the most rudimentary form and almost useless, 

 the sole organs of locomotion being the abdo- 

 minal or false legs, while in the common 

 maggots (Jig. 358) both the abdominal and 

 thoracic legs are absent, and locomotion is 

 performed equally by every segment of the 

 body. In addition to this it may be stated that 

 in some of the active larvae of the most perfect 

 Coleoptera, as in the Carabida, there is a 

 lengthened form of cord and a ganglion in 

 almost every segment of the body. Burmeister 

 found the brain and twelve sub-cesophageal 

 ganglia in the larva of Calosoma, and yet the 

 insect possesses only six thoracic legs, the 

 abdominal ones being entirely absent, excepting 

 only the caudal leg or extremity of the abdo- 

 men, in which segment there is no ganglion. 

 These facts will prove that although a concen- 

 trated form of the nervous system usually exists 

 with a more perfect development of other parts 

 of the body, it exists also when the develop- 

 ment of other parts is imperfect. It is not, 

 then, the immobility of the segments that regu- 

 lates the disappearance of the ganglia, since, 

 as Burmeister has justly remarked, there is as 

 little motion of the segments of the abdomen 

 in the perfect Carabid<s and Lucanidee, in which 

 cords and ganglia exist, as in the Melolonthidte, 

 in which they are absent. Neither is it neces- 

 sary that ganglia should be present as a means 

 of supplying energy in segments upon which, 

 as in Eristalis, the entire locomotive power of 

 the insect depends, or that when ganglia are 

 present they are necessarily connected with the 

 function of motion. 



The most concentrated form of the nervous 

 system in all its states exists in the Lamelli- 

 curnes, the Scarabocidte, and Melolontlrida ; 

 but it is remarkable that even in these the 

 development of the brain or supra-cesophageal 

 ganglia is less perfect in the larva state than 

 any of the other ganglia, and is not more 

 advanced than in the Lepidoptera, in which, 

 in the caterpillars of the nettle butterfly, Vanessa 

 iirtictf, so late as the middle of the last period 

 of the larva state we have found these ganglia 

 very distinct from each other, being only 

 approximated in the middle line by their convex 

 surfaces. Towards the latter period of the 

 larva state they become rapidly more and more 

 united, and at the time of change have formed 

 one continued mass, placed transversely across 

 the asophagus.. A similar condition of the 

 brain exists in the soft-bodied larvae of the 



