OF THE ALIMENTARY TRACT 11 



is generally alveolated, that is there exists a reticu- 

 lated network frame structure, corresponding to the 

 connective and framework tissues of higher animals. 

 This network holds the fluid substances in order and 

 allows the development of currents of interchange of 

 substances of secretion, nutrition, and excretion, in 

 other words a circulation adequate for the needs of the 

 animal. 



The center of life and its activities in protozoa is 

 the nucleus. This body is located in the endoplasm, 

 and corresponds in a general way to the nucleus of 

 the cells of higher animals in its construction, essen- 

 tial character, and manner of participation in division 

 of the organism. It has a limiting membrane enclos- 

 ing a network of (linin) fibrils, within the meshes of 

 which lies the fluid of the nucleus, and arranged on 

 this network or clinging to the rim is the chromatin, 

 the particularly essential nuclear substance. This 

 chromatin is variously distributed in different forms 

 and its arrangement is so typical in some that it is 

 used as one basis of differentiating and identifying 

 them. The common nuclear appearance of those 

 with which w^e are here concerned is that with a 

 definite rim, rounded in outline, with granules of 

 chromatin of varying sizes clinging to the inner 

 surface of the rim and also accumulated in or near 

 the center in a mass called the karyosome. The linin 

 network is more or less distinct and on its threads may 

 appear chromatin granules. 



The nucleus is necessary to the continued exist- 



