86 ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



passing thi to the exterior the renal or nephridial system. 



And fi : . t in 1 he bodies of most Metazoa hosts of permanently 



.-i-d amoebocytes cells which retain a more or less amoeboid 



i-hara. ! >le to creep about actively and to attack, and either 



-port to a position in which they are harmless, noxious 



lound their way into the body such as for example 



bes. 



individual cell of the Metazoon, just as the whole individual 



Protozoon, may be said to be aquatic in its habit, for in order to live it 



has to be in contact with watery fluid. The whole body then of the 



permeated, all its intercellular chinks are filled, by watery 



fluid, fonnin- an internal medium just as the water forms the external 



medium !>r a live-living Protozoon. This internal medium however is 



< (.>mple\ in chemical composition than ordinary water, for 



into it are !IM har-ed the various products of the metabolism of the living 



.\>m. Just as the myriads of cells which constitute the body 



bvious specializations of form and structure, so also there exist 



less obvious peculiarities in their metabolism. Consequently the 



substances which find their way into the internal medium from the 



\.irious types of cell are by no means identical but have their own special 



nties. These various substances, contributed each in its normal 



proportion, constitute, with the water into which they are discharged, 



niniusly complicated internal medium of the body. Every living 



ell in a particular species of animal is adapted to life in an internal medium 



omposition, and if any particular organ or tissue fails to 



contribute its quota, or contributes it in abnormal proportion, then the 



ML,' abnormality in composition of the internal medium is apt to 



.irmful it may be disastrous effects on the health of the whole 



body. 



COELENTERATA 



SCHEME OF CLASSIFICATION 



I. HYDROZOA. 

 A. Hydrida. 

 15. II\dromedll.sac. 



(1) (iymnohlastea (Anthomedusae). 



(2) Calyptoblastea (Leptomedusae). 



C. At .drpliac. 

 II . ACTINOZOA. 



A. A!< \<maria. 

 antharia. 



