440 Mr. Newport on the Anatomy and 



perfect and larva states of insects of that Order. Perla, with its enlarged 

 tracheae, its sacculated stomach and colon, and its more concentrated nervous 

 system, is much in advance of Pteronarcys, which retains the larva type of 

 organization in all its structures, branchial organs of respiration, a capacious 

 oesophagus and elongated alimentary canal, and more numerous and sepa- 

 rated ganglia in its nervous cord. On passing from the general conformation 

 to the details of its nervous system, Pteronarcys still preserves the same infe- 

 riority. The cephalic ganglia, which constitute the brain, have not completely 

 coalesced, as in some of the more perfect insects, but have only partially united 

 in the middle line above the oesophagus ; while the antennal ganglia in front 

 of them are also distinct and separate. The ocelli on the front and vertex of 

 the head in the perfect insect (fig. 10) are supplied by short nervous trunks, 

 which proceed directly from the cephalic ganglia (fig. 11). The anterior or 

 median ocellus is primarily a double organ. It derives its nerve from two 

 trunks, which originate one from the front of each of the cephalic ganglia, 

 and which immediately are united laterally to form the nerve to the ocellus. 

 This is the mode of origin of the anterior ocellar nerve in Pteronarcys, as I 

 have found it to be also in Hymenoptera, and other insects. The posterior 

 ocelli are supplied each by single trunks from the two cephalic ganglia. The 

 true optic nerves, which supply the compound lateral eyes of the insect, have 

 distinct gangliform enlargements at their base, and are expanded at their 

 termination into a broad retina. 



The nervous cord exhibits distinct indications of its compound structure. 

 The aganglionic portion, which I formerly described * in Lepidoptera, is very 

 distinctly seen on its superior or visceral surface, while passing over the 

 ganglia in the thoracic segments {u, v, w). It gives off a branch on each side 

 in its course between the pro- and meso-thoracic ganglia in company with 

 some organic or transverse fibres. This branch passes diagonally back- 

 wards, distributes some ramifications to the respiratory organs connected 

 with the prothoracic spiracle, and then joins the first nerve from the meso- 

 thoracic ganglion, and with it forms the anterior alar nerve that supplies 

 the muscles of the first pair of wings, thus directly associating the function 

 of respiration with that of flight. The origination of the wings, during 



* PhU. Trans. 1834. 



