GENERAL ORGANOLOGY. 121 



(4) circulatory, (5) excretory, (6) genital, (7) muscular, (8) 

 nervous, and (9) the system of sense-organs. The skeleton 

 may be absent in many animals, and the other systems 

 specialized in man may be simplified, so that, according to 

 the fundamental vital functions, the following groups of or- 

 gans can be arranged: I. Organs of assimilation (25); II. 

 Organs of reproduction (6); III. Organs of motion (7); 

 IV. Organs of perception (8 and 9). 



Vegetal and Animal Organs The organs of as- 

 similation and of reproduction (I and II) are grouped to- 

 gether as vegetal, the others (III and IV) as animal or- 

 gans. The older zoologists used to say that assimilation 

 and reproduction are functions which are common to ani- 

 mals and plants ; that, on the contrary, sensation and motion 

 are lacking in plants, and are exclusively characteristic of 

 animals. The atom of truth in the fundamental idea needs 

 reconsideration in the light of our present knowledge. 

 We have seen that the protoplasm found in plants and ani- 

 mals has not only the power of assimilation and reproduc- 

 tion, but also power of motion and of irritability. The 

 latter characteristics consequently cannot be entirely lack- 

 ing in all the plants, for they are found in the most impor- 

 tant. In fact many plants, as the mimosas, the compass- 

 plants, show great irritability ; many low plants, the re- 

 productive states of algae, move quite as actively as, or even 

 more actively than, many of the lower animals. On the other 

 hand, there are many animals which in the mature condition 

 are fixed in position like plants. ^ia.ny protozoa and zvortus, 

 most of the zoophytes, some ccJiinodcrms like the sea-lilies, 

 even many crabs, the cirripcdcs (barnacles), can change 

 their location only during the earlier stages of development, 

 in later life being limited to movements of single parts of 

 the body, the arms, tentacles, etc. In the sponges even 

 these single motions are so insignificant that they cannot 

 be seen at all by the naked eye, and scarcely even with the 

 aid of the microscope. 



Nevertheless the two terms, animal and 1'cgctaL 

 must be retained. For although motion and sensation 



