118 CLASSIFICATION OP THE ANIMAL KINGDOM. 



with three small cartilaginous teeth. Its digestive apparatus consists of a 

 stomach, with numerous lateral coecal appendages, capable of great distension, 

 and a small intestine. It breathes by means of spiracles, of which there 

 are seventeen on each side. The circulatory system is of a complex nature, 

 and is provided with veins and arteries, but there is no heart; while the 

 nervous system is composed of a series of small ganglia connected by 

 filaments, the anterior pair being larger than the rest, forming a rudimen- 

 tary type of the brain of vertebrate animals. They are possessed of eight 

 or ten simple eyes, and as regards their generative organs, they are her- 

 maphrodite, but not self-impregnating. 



The Abranchia terricola > or Earth-worms, live beneath the ground, either 

 inland or amongst the mud by the sea-shore. They move along by means 

 of a number of sharp spines. Their digestive apparatus consists of a straight 

 and capacious alimentary canal, with an oesophagus and gizzard. Their 

 circulatory system is somewhat similar to that of the Leech, but is more 

 elaborate. Respiration is effected by the copious distribution of the blood 

 to the integument of the body, and also by the admission of air by means 

 of stigmata. The generative organs of the Earth-worm are situated in 

 the anterior part of the body, their position being indicated externally by 

 a considerable enlargement or swelling, which extends from the seventh 

 to the fourteenth segment, counting from that in which the mouth is 

 situated. They are hermaphrodite, but not dioecious; and the young are 

 produced from eggs. Some species of Annelida are also reproduced by 

 spontaneous division; and the Earth-worms, though they cannot be multi- 

 plied by mechanical division, yet have the power of reproducing small 

 parts of their bodies. 



The second order of Cuvier, the Dorsibranchia, are all inhabitants of 

 the sea, and, as their name implies, they breathe by means of external 

 branchial tufts, or tubercles, of singular and variable construction; in some 

 cases these organs being spread over the entire body, in others confined 

 to a few of the segments. They have mouths of a peculiar structure, 

 capable of being turned inside out, and armed, in some species, with 

 powerful teeth. The alimentary canal is similar to that of the abranchiate 

 worms, as is also the general course of the circulatory system. The organs 

 of reproduction are but little understood; the species of Nereis seem to be 

 self propagating by spontaneous division; and, says Professor Jones, "some 

 curious speculations have been entertained by continental writers relative 

 to this mode of propagation. The tail of the original Nereis is still the 

 tail of its offspring, and however often the body may divide, still the 

 same tail remains attached to the hinder portion, so that this part of the 

 animal may be said to enjoy a kind of immunity from death." 



The Tubicola, Cuvier's third order, which inhabit pipes or tubes of 



