364 LECTURE XVT. 



a slight enlargement. Two short and thick optic nerves pass from 

 the sides of the brain to form the ganglions supplying the large com- 

 pound eyes. The stomato-gastric nerves arise, one on each side, near 

 the optic nerves. The oesophageal columns are short, and directly 

 converge to the inferior cerebral ganglion, which gives two large and 

 several small nerves to the jaws: it is situated in the head. Two 

 long and parallel columns extend to the first thoracic ganglion, which 

 transmits long and large nerves to the formidable prehensile anterior 

 pair of legs. The second thoracic or elytral ganglion is at a great 

 distance from the first, and much nearer the third or alar ganglion. 

 Anastomosing branches connect the nerves which these ganglions 

 respectively distribute to the elytra and wings. The Mantis is 

 chiefly remarkable for the great length of the ventral chords con- 

 necting the brachial with the elytral ganglia, and which renders 

 them favourable for minute analysis of their structure. Anterior 

 and posterior columns, or divisions analogous to those in the spinal 

 marrow of higher animals, cannot be distinguished. The so-called 

 sensorial tract is confined to accumulations of nervous matter at the 

 origin of the nerves to the locomotive organs. 



Experiments in which the body of the living Mantis has been so 

 divided that a segment with one of these ganglionic enlargements 

 and the locomotive organs it supplies has been detached from the 

 rest, illustrate the functions of the aggregated centres of nervous 

 matter in relation to their power of receiving and transmitting im- 

 pressions, so as to maintain the order of action of such detached 

 organs upon the application of a stimulus, for a considerable period 

 after the mutilation. 



The jaws of the separated head of a Mantis bite forcibly the stick 

 which is held to them. The formidably armed prehensile legs in 

 like manner wound the finger tliat touches them, when the segment 

 of the body supporting them is separated from the head and the rest 

 of the trunk. And if decapitation or amputation of the prothorax be 

 neatly performed on the living insect, while in its natural and 

 ordinary position, perched by its middle and hinder pairs of legs 

 upon a twig, the rest of the trunk does not fall to the ground, but is 

 maintained for a certain period in that posture, which it even 

 recovers by actions of the wings, when the balance is slightly and 

 purposely disturbed. 



The super-oesophageal or cerebral mass in insects obtains its largest 

 development in the dragon-fly {Libellula), which from the size and 

 perfection of its organs of vision, its great and enduring powers of 

 fliglit and predatory habits, may be regarded as the eagle of insects. 

 From the side of each of the superior lobes of the brain, the optic 



