THE PKOTOZOA (continued) 



SECTION L. THE INFUSORIA OR CORTICATA HETEROKARYOTA l 



THIS group is clearly marked off from other Corticata by the 

 occurrence of cilia, suckers, or tentacles in the active phase of life 

 of all species. A character which is of far greater morphological 

 importance, however, is the presence in each individual of two 

 distinct nuclear elements called .the meganucleus and micronucleus 

 respectively. 



The group is divided into two classes : 



THE CILIATA (Ehrenberg). 

 THE ACINETARIA (Lankester). 



The Ciliata are either free or fixed forms with cilia disposed in 

 tracts or bands on the cortex. 



The Acinetaria are fixed or sedentary forms provided with 

 suckers or tentacles. They give rise to free-swimming individuals 

 which are ciliated. 



HABITS. The habits of the animals included in this group are 

 very variable, and may be conveniently studied as arranged in 

 five categories, the free-swimming habit, the creeping or crawling 

 habit, the stalked fixed habit, the epizoic habit, the endozoic habit. 



The Heterokaryota with free -swimming habits principally 

 belong to the group of the Ciliata. They may be found in pure 

 pond water (Spirostomum, Paramoeciwn sp., etc.), swimming freely 

 near the surface or hovering about the mud at the bottom, or even 

 coursing about the water in the intermediate depths. A consider- 

 able number of genera are marine. 



Their food consists principally of minute animal and vegetable 

 organisms that they find floating in the water, but they will also 

 seize and devour particles of organic matter set free by the 

 dissolution of animal or vegetable bodies after death. Some 

 species appear to find their maximum vitality in water containing 

 putrefying matter, in which case their food consists chiefly of 



1 By S. J. Hickson, F.R.S. 



