60 INTRODUCTION. 



neys, that secrete the urine, and the greater portion a bladder 

 or resevoir for this excrementitious humour. The sexes are 

 always separate; the female has one or two ovaries from 

 which the eggs detach themselves. The male fecundates them 

 with the spermatic fluid, but the mode of impregnation as 

 well as other phenomena of generation, greatly varies. 



The muscles, independently of those that form the heart, 

 and those that belong to the skin, the mucous membrane and 

 the senses, are very numerous, and are inserted into internal 

 bones, moving on each other. All such as have lungs, have 

 also a larynx, although all have not a voice. The senses consist 

 of two eyes, two ears, the nose, the tongue and the skin; this 

 membrane being besides provided with several protecting 

 parts, but it is essentially the nervous system which peculiarly 

 distinguishes the vertebrata. In the invertebrate animals the 

 same nervous enlargements, more or less separated, send fila- 

 ments indifferently to the organs of the animal, as well as the 

 vegetative functions ; here, on the contrary, besides those gan- 

 glions whose filaments are restricted to the organs of the ve- 

 getative functions, there is a particular centre with which these 

 enlargements communicate, and from which originate or where 

 terminate the nerves of the organs of sensation and motion. 

 This centre, perfectly symmetrical, consisting of a thick cord 

 enclosed in the spine, is extended into the cranium, where it 

 presents various enlargements, and is surmounted by two 

 complex nervous organs, called cerebellum and cerebrum. 

 This nervous centre is enveloped by bones firmly united with 

 each other, that defend it from external injuries. This func- 

 tion of the bones may be regarded as one of the most impor- 

 tant they possess. 



54. Besides the kinds of humours and organs common to 

 all, or at least to the generality of animals, some are found 

 among the vertebrata, which have no existence in the others; 

 these are the red blood, the lymphatic and chyliferous vessels, 

 bones, ligaments and tendons, and the serous and synovial 

 membranes. 



In all the invertebrata, the nutritious liquid is of one single 

 colour, and that white or bluish, if we except the annelides 



