192 LECTURE XVI. 



LECTUEE XYI. 



IIs^SECTA. 



Although spontaneous locomotion is the peculiar attribute of the 

 Animal Kingdom, we have seen that the lowest members, the Zoophy- 

 tes as they were termed, were, for the most part, fixed and motionless, 

 like plants : we have seen that the first manifestations of locomotion 

 were of the feeblest and simplest character, a rowing of the body 

 through an element of equal density with itself, or a trailing of the 

 body along the ground, which supported it at every point. As we 

 advanced to the survey of the Articulate series of animals, we saw 

 the integument progressively hardened, divided into segments which 

 were united by flexible joints ; at length supported upon moveable 

 jointed limbs, consisting of hollow columns of integument hardened 

 into a dense exterior crust, capable of serving the office of levers 

 and fulcra, whereby the animal could raise its belly from the dust, 

 and swiftly traverse the surface of the ground. 



We now come to a class oi Articulata, in which the highest problem 

 of animal mechanics is solved, and the entire body and its appendages 

 can be lifted from the ground and be propelled through the air. The 

 species which enjoy this swiftest mode of traversing space, breathe 

 the air directly : but their organs of respiration are peculiarly modi- 

 fied in relation to their powers of locomotion ; they consist of innu- 

 merable tracheae commencing from lateral pores called stigmata, or 

 by anal tubes, which are ramified through and over every tissue and 

 organ of the body. The nervous system is homogangliate ; the 

 organs of sense include two jointed antennae and two compound eyes ; 

 the skeleton is principally external, and cut deeply into segments, 

 whence the name of the class Insectn. 



Not every Insect, however, has the power of flight, nor any Insect 

 save in its last and most perfect state ; many undergo most remark- 

 able transformations before they acquire their wings, and although 

 some Insects, which ultimately are so endowed, undergo a less 

 amount of change, yet the metamorphoses are always least remark- 

 able in the apterous species. 



Of these lowest members of the class of Insects, many have more 

 than three pairs of legs, have sometimes indeed eighty pairs and 

 upwards in their mature state : metamorphic development exhausts 

 itself, as in the Anellides, in the successive acquisition of new segments 



