THE METAMORPHOSIS. 439 



the largest, and consists of the throat as the base, and of the two large 

 temples which meet at the vortex, as the arch. Between them a 

 triangular piece lies anteriorly and above, the clypeus, which has the 

 eyes at its lower angles, and the mandibles at its base ; beneath, the 

 chin lies next to the throat, which thus closes the second arch indicated 

 by the clypeus. Both together form the second vertebra ; it enlarges 

 during the metamorphosis, and thereby pushes back the arch of the 

 posterior vertebra. The oral organs are attached to it, and it contains 

 within it, the cerebrum, or the ganglion of the eyes. The clypeus is 

 the body, or vertebra itself, the branches of which, or arch, bend 

 downwards to the chin ; the chin itself is the upper plate of the ver- 

 tebral ring, or part corresponding with the sternum. The mandibles 

 hang attached as limbs to this vertebra. The eyes also are situated 

 upon the anterior vertebra, and which indicate posteriorly its limits, 

 in as much as their horny external surface appear, as it were, introduced 

 in the free space between the two vertebrae, or rather have separated 

 them from each other. Thus, therefore, the optic nerve passes just 

 in the same manner between the two vertebrae, as the nerves of the 

 spinal cord pass between the arches of the vertebrae. The posterior of 

 these vertebral arches, namely, that for the cerebellum has, as well as 

 the thoracic vertebrae, its internal processes, or the second ring, which 

 corresponds with the true vertebral arches. It, therefore, originates as 

 a furcate process from the throat, and embraces the cerebellum with its 

 branches. When these branches unite they form the tentorium, or the 

 small band which divides the occipital aperture into two halves. But 

 we do not find anything analogous in the first vertebra ; did it exist, it 

 would necessarily proceed from the clypeus or the forehead. 



258. 



The opinion, therefore, that the trunk of the insect is formed upon 

 the same type as that of the vertebrate animal is thus corroborated : 

 we have exhibited even the same analogy in the head. The chief 

 difference of the two organisations, however, consists in the back 

 in the insect being turned downwards, but in the vertebrate animal 

 upwards. What Von Bar* cites as a proof in opposition to this 

 assertion, viz. that the upper side of insects is the distending side, 

 the lower the bending side, and that, therefore, as in the vertebrata, the 



* Entvvickelungsgeschichte der Thierc, p. 246. 



