20 NATURE AND OBJECTS OF PHYSIOLOGICAL SCIENCE. 



notice the tendency to "vegetative repetition;" for it may be observed 

 in many animals which can be divided without the destruction of their 

 lives, especially among the Radiated, and the lower Articulated tribes. 

 Where such a repetition exists, some of the organs may be removed with- 

 out permanent injury to the structure ; their function being performed 

 by those that remain. Thus it is not uncommon to meet with specimens 

 of the common five-rayed Starfish, in which not only one or two, but even 

 three or four, of the arms have been lost without the destruction of the 

 animal's life ; and this is the more remarkable, as the arms are not 

 simply organs of locomotion or prehension, but contain prolongations of 

 the stomach. In the bodies of the higher animals, however, where there 

 are few or no such repetitions (save on the two sides of the body), and 

 where there is consequently a greater diversity in character and function 

 between the different organs, the mutual dependence of their actions upon 

 one another is much greater, and the loss of a single part is much more 

 likely to endanger the existence of the whole. Such structures are said 

 to be more highly organized than those of the lower classes ; not because 

 the whole number of parts is greater, for it is frequently much less ; 

 but because the number of dissimilar parts, and the consequent adap- 

 tation to a variety of purposes, is much greater, the principle of divi- 

 sion of labour, in fact, being carried much further, a much larger class 

 of objects being attained, and a much greater perfection in the accom- 

 plishment of them being thus provided for. 



6. Keeping in view, then, what has just been stated in regard to the 

 divisibility of a Tree or a Zoophyte into a number of parts, each capable 

 of maintaining its own existence, we may trace a certain gradation from 

 the condition of the Mineral body to that of the highest Animal, in 

 regard to the character in question. Thus, the individuality of a Mi- 

 neral substance may be said to reside in each molecule ; that of a Plant 

 or Zoophyte, in each complete member ; and that of one of the higher 

 Animals, in the sum of all the organs. The distinction is much greater, 

 however, between the lowest organized fabric and any mineral body, 

 than it is between the highest and the lowest organized structures ; for, as 

 we shall hereafter see, the highest and most complicated may be regarded 

 as made up of an assemblage of the lowest and simplest ; whose structure 

 and actions have been so modified as to render them mutually depen- 

 dent; but which yet retain a separate individuality, such as enables 

 them to continue performing their functions when separated from the 

 mass, so long as the proper conditions are supplied. 



7. Between the very simplest Organized fabric, and every form of 

 Mineral matter, there is a marked difference in regard to intimate struc- 

 ture and consistence. Inorganic substances can scarcely be regarded as 

 possessing a structure ; since (if there be no admixture of components) 

 they are uniform and homogeneous throughout, whether existing in the 

 solid, the liquid, or the gaseous form ; being composed of similar parti- 

 cles, held together by attractions which affect all alike. Far different 

 is the character of Organized structures ; for in the minutest parts of 

 these may be detected a heterogeneous composition, a mixture of solid 

 and fluid elements, which are so intimately combined and arranged, as 

 to impart such peculiarities to the tissues, even in regard to their physi- 



