vidual organs, from their highly complicated and elaborate 

 structure in Quadrupeds, to their simplest forms, and their 

 total disappearance in the lower orders. It shows that, 

 notwithstanding the highly complicated organization we 

 observe in the more perfect animals, and the intimate con- 

 nexion which subsists between all their parts, not one of all 

 their organs is universal in the Animal Kingdom, or essen- 

 tial to the phenomena of animal life. The whole skeleton, 

 the solid frame-work of the body, destined to give 

 strength, form, and support to the entire machine, disap- 

 pears in the class of Molluscous Animals, as in the Doris, 

 Tritonia, Eolis, &c. The muscular system, so essential 

 to all the voluntary and involuntary movements of the 

 higher classes, entirely disappears in the class of Radiated 

 Animals, and with it every trace of nervous system which 

 we are apt to suppose essentially connected with all the 

 motions and functions of animals. The brain, so inti- 

 mately connected with the phenomena of mind, after 

 dwindling into the form of a few separate ganglia placed 

 on the oesophagus, and connected only with the function 

 of digestion, disappears from the Animal Kingdom. The 

 heart, the great centre of the circulation, after diminishing 

 successively the number of its cavities, from four to one* 

 in the higher classes of animals, disappears among insects. 

 The blood-vessels also cease to exist, and, with them, all 

 circulating motion of the blood, as in most Radiated 

 Animals, and in the whole class of Zoophytes. The func- 

 tion of respiration is intimately connected with the circula- 

 tion of the blood, and its organs, after undergoing various 

 modifications of form, suited to the different media in 

 which the animals live, cease to belong to the system. 

 Although the function of secretion is performed by animals 

 very low in the scale, all distinct glandular organs for 

 its performance are lost long before the total disappearance 

 of an internal digestive cavity. Many of the lowest Zoo- 

 phytes, which have no internal digestive sac, and no polypi, 

 (which are only superficial digestive cavities,) absorb their 



