222 LECTURES ON BIOLOGY 



In the other orders of the Infusorians the differentiation incilia- 

 tion has made very considerable progress. We see that the cilia 

 are here used for the most diverse functions swimming, crawling, 

 jumping, wafting-in food, etc., and are transformed according 

 to their work. Perhaps the most remarkable transformation 

 which the cilia have undergone is observed in the shell-animalcule 

 (Stylonychia mytilus) which I have already mentioned. Here some 

 of the cilia of the ventral surface i.e., the surface which during 

 locomotion is opposite the object on which they crawl, and where 

 is found the mouth-aperture have assumed a strong, rigid ' slate 

 pencil' form, while others have become cirrhous. These simple 

 ' legs ' are skilfully used by Stylonycliia for running along the 

 ground when in search of prey. 



But let us return to the Paramceciiun. At the bottom of the 

 peristome- field we observe a small round orifice, the ' mouth ' 

 of the cell. Food, which chiefly consists of bacteria and similar 

 minute organisms, is wafted into this mouth by means of the cilia, 

 and reaches through the orifice the pharynx of the animalcule, 

 a short canal bent in the shape of an S, which leads direct into 

 the body-plasm. The indigestible parts are passed out through 

 a special aperture. The very complex contractile vacuoles 

 serve as organs of excretion. They are no longer the primitive 

 vesicles of the Amoeba, for we can here distinguish between an 

 inner vesicle and a canal - system, extending from it to the 

 protoplasm. The canals collect the used-up fluid from the entire 

 body, conduct it to the central vesicle which, in consequence, 

 swells gradually until it reaches a considerable size. Suddenly 

 it collapses by passing its contents to the outside through a 

 minute pore. This process is repeated at regular intervals. 



If the organella mentioned before demonstrated already an 

 enormous progress in the development as compared with the 

 Rhizopods this distance will be still further increased when we 

 consider the other differentiations of the protoplasmic body. In 

 Param&cium we are able to distinguish an ectoplasm from the 

 endoplasm. The first, again, is divided into a more solid cover, 

 the pellicle, under which we can distinctly perceive a thin 

 layer of a honeycombed structure. Below this lies the so-called 

 1 cortical plasm,' a fine hyaline mantle which is sharply separated 

 from the endoplasm and can, moreover, be distinguished from it 



