24 DIFFEKENCES BETWEEN ANIMALS AND PLANTS. 



are under the empire of a ganglionic cord, similar to the 

 sympathetic nerve in man. These two great classes never 

 present an internal articulated skeleton ; their muscles are 

 attached to the skin, which is more or less indurated. The 

 Crustacea and mollusca have a heart and blood-vessels, for 

 propelling and circulating their nutritive fluids, with branchiae 

 for aquatic and pulmonary sacs for seriform respiration. In 

 the arachnida, insects, and annelides, the circulation is carried 

 on by a pulsating dorsal vessel, and respiration is accomplished 

 by sacs, branchiae, or trachiee, that ramify, like blood-vessels, 

 through every part of the body : their jaws move on a hori- 

 zontal plane, and many of them are provided with a proboscis 

 or a suctorial apparatus. They possess the senses of vision, 

 and even those of smell and hearing ; touch and taste, being 

 refined modifications of sensibility, are enjoyed in a greater or 

 less degree by ah 1 animals. The reproductive organs in the 

 acephalous mollusca (as the oyster) are united in the same in- 

 dividual : they are separate, however, in the gasteropoda (as 

 the snail) and cephalopoda (as the cuttle-fish), as well as in 

 the Crustacea and insects. 



[ 72. This division of the animal series is analogous to 

 the monocotyledonous plants. The marrow or pith is inter- 

 woven with their vegetable fibres, as the nervous system 

 is disseminated by ganglia through the bodies of the inver- 

 tebrata ; there is no osseous skeleton in the one, nor is there 

 any true wood in the other, but in both the circumference is 

 more solid than the centre. We see among some families of 

 this section (as the grasses, lilies, and palms, &c,, the same as 

 among insects, Crustacea, and annelides), the integument more 

 or less indurated, and in some families containing a quantity 

 of silicious particles, just as the external skeleton of insects is 

 composed of peculiar animal substances, termed chitine and 

 coccine, and consolidated by minute proportions of the phos- 

 phates of lime, magnesia, and iron ; or that of Crustacea, which 

 is hardened with nearly half its weight of the carbonate of lime, 

 and a considerable proportion of the phosphate, with traces of 

 magnesia, iron, and soda. The knotty-jointed stems of many 

 grasses represent the articulated bodies of worms, Crustacea, 

 and myriapods. Many families of this division produce seed 

 only once in their lives, like some worms and insects which cease 

 to exist after having deposited their ova. Their leaves are 



