DTFFEEEXCES BETWEEX AJTIMALS A1SD PLANTS. 23 



is sometimes furnished with small cceca ; they have no per- 

 ceptible blood-vessels nor special organs for respiration and 

 reproduction ; they are all aquatic, and are analogous to the 

 lowest division of the vegetable series, the acotyledonous or 

 cellular plants, both in form, consistence, and chemical com- 

 position. 



[69. The acotyledons all possess a soft, pulpy tissue of 

 the most simple organisation, deprived of fibres. The repro- 

 ductive organs are altogether absent, or are united on the same 

 individual ; they have no medullary substance, and are merely 

 expansions of simple cells, in which no special organs are de- 

 veloped for any of the functions. 



[ 70. The second division of the animal series comprehends 

 all those in which we find the nervous system disposed in cords 

 in a body more or less symmetrical, extending from the head 

 to the posterior extremity, under the intestinal canal. In all 

 the classes of this great section the nervous trunks lie on 

 the ventral surface of the body, and are provided at intervals 

 with a number of ganglia, from which leashes of fila- 

 ments emanate to supply the different organs. The nervous 

 centre we call the brain, is formed in them of a double gan- 

 glion, situated above the esophagous ; from it two branches 

 arise to unite in ganglia situated below that tube, thus em- 

 bracing the esophagous like a necklace or collar : from this 

 nervous circle filaments proceed to be distributed to the different 

 organs of the body. In all the mollusca, the nervous system 

 preserves this general character ; but among the articulata, as 

 Crustacea, insects, and annelides, each ring of the body pos- 

 sesses a ganglion, which distributes filaments to the organs 

 contained therein. The number of ganglia in the series cor- 

 responds to the segments comprised in the length of the 

 body, the whole being connected together by a double cord, 

 emanating from the lateral parts of the esophagean gan- 

 glion. From this disposition of the nervous system, life is 

 not confined to a single centre (as in the vertebrata), each 

 ganglion presiding, as it were, over the vital manifestations of 

 the organs proper to the individual segments : it is thus 

 they can reproduce many important parts that may have been 

 removed, or lost by accident, as the claws of the crab and 

 lobster, &c. 



f 7 1 . The nutritive functions of the mollusca and articulata 



