404 MR. NEWPORT ON THE NERVOUS SYSTEM OF THE SPHINX LIGUSTRT. 



feet state) are of the greatest importance to the insect ; since if these be closed, the 

 insect soon becomes axphyxiated when placed under water; but if the anterior 

 spiracles be left exposed while the remaining ones are submerged, it will live, and 

 remain active for a great length of time. Their importance is also shown in their 

 form and size in the perfect insect. It is in the anterior, this very part of the body, 

 that we find the greatest abundance and complexity of respiratory nerves, even in 

 the larva, where there scarcely seems more occasion for a greater number of respira- 

 tory nerves than in the abdominal segments. It is around the spiracles in this part 

 that the respiratory nerves divide, and pass to many muscles which are associated 

 with those of the spiracles in the function of respiration in the perfect insect ; and 

 these are muscles which are to act upon the future wings. Now the action of these 

 very muscles, which elevate and expand the wings at the instant of flight, is an act 

 of inspiration, during which the spiracles are opened, and the air, rushing into them, 

 fills the air-bags and tracheae over the whole body, juSt the same as in birds, as 

 remarked by Professor Grant, the muscles of the chest and wings are associated 

 simultaneously in action with those of the glottis and tracheae, and exactly the same 

 as the arms and muscles of the chest in man, and the anterior extremities and 

 muscles of the chest in quadrupeds, are influenced at the instant of making any 

 sudden or great exertion. 



It is also remarkable that these nerves in general appear to be developed in size in 

 proportion to the quantity of respiration of the insect. Thus, in the larva of the 

 Blood Beetle, Chrysomela tenebricosa, Linn., and in the Carabi, they are exceedingly 

 small ; while in the Sphinx and other insects that are capable of powerful and long- 

 continued flight, respire large quantities of atmospheric air, and have the organs of 

 respiration exceedingly large, they have arrived at their maximum of development. 



During the development of the Sphinx, the respiratory nerves undergo a curious 

 change of situation, which certainly indicates that they are not simply nerves of 

 motion, but are for an especial function. In the larva they are situated very close to 

 the anterior part of the ganglia, but in the perfect insect they have moved forwards 

 very nearly half way between the ganglia. Now it is well known that during deve- 

 lopment there is a tendency in nerves to approach and unite with each other, the 

 lateral cords and ganglia are more closely approximated, and the ganglia in the ante- 

 rior part of the body approach and coalesce into one mass. But instead of all the 

 transverse nerves uniting with the nerves from the ganglia, which, had they been 

 simple nerves of motion, we should expect they would have done, we find them in 

 the abdomen, carried forwards in the segments, and distributed separately to the 

 same muscles as those from the ganglia. 



Another striking fact indicative of their separate function is their being distributed 

 largely, even in the larva, to the double rooted nerves for the future wings, and but 

 slightly, so far as can be discovered, to the primary organs of locomotion, the legs. 

 The nerves to the legs come directly from the gangliated cords, and communicate 



