448 PHYSIOLOGY. 



in insects, and its deficiency explained from the imperfection of their 

 nervous system. But the muscular and nervous system of insects is as 

 perfect as that of the Cephalopoda, and there can be no objection to 

 admit it in the former, since it has been proved to exist in the latter *. 

 We undertand in this oscillation an undulating motion of the fibres, 

 which is seen together with the contraction, and which, for instance, 

 exhibits itself in partially pressed muscles, as a trembling motion which 

 frequently seizes the entire limb. The incessant vibrating motion in 

 many parts of the body of many insects, for instance, the motion of the 

 antennae in the Ichneumonodea, the trembling of the Avings in repose, 

 the palpitation of the extremities of the feet in Chironomus, c., 

 appear to be less the result of voluntary muscular motion than of the 

 oscillation peculiar to all perfect muscular substance. 



263. 



This muscular activity is therefore the foundation of all the motions 

 exercised by insects. These motions may be referred to four principal 

 kinds, namely, walking, jumping, swimming, and flying. But few 

 insects are restricted to the first and most simple of these motions, the 

 majority possess the power of flight in addition ; some can only walk 

 and leap, as the flea ; some can walk, leap, and fly, as the grasshopper; 

 many can walk, fly, and swim ; whereas there are none which possess 

 the power of swimming and flying in conjunction. Many larvae can 

 only walk and swim, others creep and swim ; no perfect insect, how- 

 ever, possesses the last mode of motion exclusively. 



If we now investigate the first, most simple, and most universally 

 distributed of these modes of progression, walking, this also may be 

 subdivided into several kinds, from the structure of the motive appa- 

 ratus. The first, and most simple, which is the progression of maggots, 

 without the help of feet, and is properly merely an advance upon the 

 ventral surface, is a sort of slow creeping. The maggot thus progresses 

 by means of the longitudinal contraction of its body, whereby the 

 distended and, as it were, swollen head is pushed onwards, this then 

 affixes itself by means of the lower and strongly projecting ventral 

 surface of the first abdominal segment, which appears to act something 

 like a sucking cup, and then draws the body as far as possible after it. 

 The posterior extremity, which in general is furnished with distinctly 



* K. A. Rudolph! Grundrisz der Physiologic, vol. ii. part i. p. 290, 294. 



