THE METAMORPHOSIS. 437 



the Arthrozoa the vertebra lie upon the ventral side, and in the Osteozoa 

 upon the dorsal. This arises from the situation of the nervous cord ; 

 if this lie upon the ventral side it then attracts the vertebrae to it, for 

 it is the earlier, they being formed around it. The nervous system in 

 general, as well as every individual nerve, seeks the best protected 

 parts, therefore, in the Gastrozoa, as well as in the Arthrozoa, its main 

 stem lies at the ventral surface, that it may conceal itself beneath the 

 other organs. If, then, the ganglionic ventral cord of the Arthrozoa be 

 analogous to the spinal cord, or as others prefer considering it, to the 

 dorsal ganglionic chain lying contiguous to the vertebrae, which may be 

 doubted since the discovery of a distinct nervus sympathicus proceeding 

 directly from the brain ; then the encompassing parts of the skeleton 

 will necessarily be analogous to those parts of the skeleton of the ver- 

 tebrata, which inclose that cord. But we prefer considering the ventral 

 cord of the Arthrozoa as the true spinal cord, from its passing within 

 the canal formed by the horny skeleton, and not contiguously, as would 

 necessarily be the case upon the adoption of its identity with the dorsal 

 ganglionic chain. According to this representation, therefore, insects 

 run with their back turned forwards, or rather underwards, and what 

 is called back in them is the true ventral side. This idea has been 

 long since suggested, and was immediately, like everything that diverges 

 from common views, strongly disputed ; but the proofs cited in opposi- 

 tion do not appear tenable, as will be evinced by what follows in sup- 

 port of our opinion. 



The situation of the intestines perfectly confirms our view. That 

 organ which lies most approximate to the vertebral column of the ver- 

 tebrata is, with the exception of the vessels which are deficient in 

 insects, the oesophagus and the intestinal canal ; even so in insects, it 

 lies immediately over the nervous cord, directly upon the inner horny 

 arch when it is closed, or still between its branches. In the vertebrata 

 next to the intestinal canal proceeding from the back towards the belly 

 we find the lungs and the heart in the thorax, in the ventral cavity the 

 intestine touches the ventral surface, in the pelvis the sexual organs 

 namely, the gravid uterus, lie in front of it. We find exactly the same 

 arrangement in insects : the lungs are omitted, as they are universally 

 distributed ; in the thorax proceeding from the back towards the breast 

 we find the heart with its large vessels. In the ventral cavity, whither 

 the heart also extends, it is likewise placed externally, and indeed the 

 return of the aorta to the back is indicated in the two main currents 



