210 LECTURE XVI. 



disappear ; the fifth blends with the fourth, and the third with the 

 second ; thus leaving four ganglions in the abdomen and two in 

 the thorax (^fi(j. 104-.). Corresponding changes take place in the 

 cerebral portion of the nervous system. The maxillary ganglion de- 

 creases with the diminution and change in the maxillary apparatus. 

 The oesophageal collar contracts, as does the canal which it surrounds. 

 The brain enlarges, having to supply organs of sense, especially those 

 of sight, which are perfected to correspond with the acquisition of 

 new and improved locomotive forces. Analogous changes we may 

 naturally conclude to take place in other orders of insects ; and we 

 find, indeed, in some of these that the nervous system continues sta- 

 tionary at stages of development which are progressive and transitory 

 in the Lepidoptera, and that further concentration is discovered to 

 have taken place in the Melolontha, Cicada, Nepa, &c., than that 

 which constitutes the highest stage observed by Heroldt and Mr. New- 

 port in the Lepidoptera. The marvel is, that these changes, due in 

 part apparently to mere mechanical influences, should be so regular, 

 so orderly, so admirably adapted in their final results to the general 

 condition and exigencies of the perfect insect: one might have sup- 

 posed that the particles of the soft and semi-fluid nervous matter, 

 squeezed by the pressure of the surrounding parts, when the body 

 seems to be, as it were, contracted by an universal spasm, would be 

 irregularly dislocated or aggregated into one or more masses ; but, 

 on the contrarj', we perceive the nervous particles moving forwai'ds 

 and I'e-arranging themselves in orderly groups, definite in their forms, 

 in their proportions, and in their relative positions ; these being ap- 

 parently regulated by a law of prospective arrangement and arranged 

 precisely in those situations where the greatest supply of nervous 

 energy is required to radiate from them in the active and perfect 

 insect. 



An idea of the situation and degree in which the sense of touch is 

 exercised in insects may be formed by observing the modifications of 

 the different parts of the integument, the papillae, or folds upon its 

 surface, the hairs, plumes, or soft jointed organs developed from par- 

 ticular parts of the body. The soft balls on the feet of grasshoppers, 

 the pulvilli and suckers on those of flies, the soft, setaceous, or 

 plumed antennae, and, above all, the palpi, often provided with a ter- 

 minal vesicle, present the requisite physiological conditions of the 

 organ of touch. Although another sense, and most probably that of 

 hearing, may reside in the antennae, yet no one can witness the use of 

 these organs by bees and ants, the exploratory actions of those of the 

 ichneumon and of many other insects, without I'ecognising in them 

 instruments of the tactile faculty. 



