THE FLY. 61 



a pair to the anterior legs, another to the wings, a 

 third pair to the second legs, a large pair (the largest 

 of all) to the halteres, and two nerves to the posterior 

 legs. Besides these, the thoracic ganglion also gives 

 out a bundle of nerves (arranged bilaterally) into the 

 abdomen ; a single one, however, passing through the 

 centre of that section of the body, at the termination 

 of which it is forked, and the two extremities pro- 

 ceed to the reproductive organs on each side. Thus 

 you win perceive that every portion of the Fly's body, 

 every organ and member, is provided with its special 

 nerve ; and if we now compare this portion of its phy- 

 siology with the nervous system of the Worm (Let- 

 ter III.), and of the Fly itself in its larval stage, we 

 shall find the comparison of their structure to be 

 interestiQg and instructive. The brain of the Worm 

 resembles that of the Fly, and also gives off two 

 chords, which unite and pass along the ventral sur- 

 face of the body. In each ring we found bilateral 

 branches proceeding from the central chord; and 

 these branches being often repeated, and of a uni- 

 form size, afford evidence, upon the principle already 

 referred to*, of the humble organization of the 

 Worm. 



If we next take the larva, or grub of the House- 

 fly, the body of which also consists of soft rings, as 

 in the Worm, we shall find in each ring, and situated 



* In treating of the eye of tlie Fly, we explained that a repe- 

 tition of similar parts was an evidence of its low organization, 

 as compared with the higher animals, 



