358 LECTURE XVI. 



the ganglionic and nonganglionic portions of the true nervous axi^, 

 the same physiological reasonings Avill apply as have led to the conclu- 

 sions ah'eady given respecting their office in the crustaceous animals. 



Of the four nerves which come off from the sides of the ganglionic 

 portions of tlie columns, the second, which is principally distributed 

 to the muscles of the corresponding pair of legs, arises in a great pro- 

 portion from the ganglion itself. The first and third nerves, which 

 are smaller than the second, supply the muscles and integuments of 

 the segment. The fourth pair of nerves passes to the breathing 

 pore and to the integument. This, therefore, must be regarded as the 

 respiratory nerve. The stomato-gastric nerve is a distinct system 

 connected with the anterior ring or brain. 



Thus in the Myriapodous insects we find that although the prin- 

 ciple of irrelative repetition prevails in the nervous system as in the 

 skeleton and locomotive instruments, yet it does not prevent the 

 recognition of the leading physiological divisions of that system. We 

 have, for example, the super-oesophageal or cephalic portion, which is 

 subservient to the functions of the special organs of the senses, and is 

 the centre whence voluntary impulse may be directed along the non- 

 ganglionic tracts of the nervous axis, and to which ordinary sensa- 

 tion may be transferred by similarly uninterrupted nervous filaments. 

 We have, secondly, a large sub-oesophageal mass, which, originating 

 the nerves analogous to the fifth pair, for the masticating organs and 

 other parts of the head, may be regarded as analogous to the medulla 

 oblongata. In the abdominal chords and ganglions we have the re- 

 quisite machinery for the automatic reception and reflexion of stimuli, 

 independently of sensation and the will ; and to these are superadded 

 internuntiate and uninterrupted chords, for bringing the body under 

 the dominion of the will, and for producing harmony and consent of 

 action throughout its extent. The special nerves to the respiratory 

 system, and the stomato-gastric nerves, complete this already compli- 

 cated nervous system. 



In the hexapod insects the nervous system differs chiefly from that 

 in the Myriapods in having its primary divisions more definitely de- 

 veloped, and in manifesting degrees of concentration corresponding 

 with the increase of bulk and strength in particular parts of the trunk, 

 and in the locomotive organs appended thereto. Most insects, how- 

 ever, commence their career as worms ; the high form which they are 

 ultimately destined to attain in the articulate series is at first masked by 

 the guise of an Anellid or Entozoon. Some insects retain their larval 

 or vermiform state much longer than others ; and after passing a great 

 proportion of their lives under this form, fall into the state of the pupa, 

 or chrysalis, — relapsing, as it were, a second time into the condition of 



