CHAPTER XXIII 



HETEROKARYOTA 



Preliminary — Heterokaryota — Ciliata — Balantidium — Nyctotherus — 



References, 



DIVISION B. HETEROKARYOTA Hickson, 1903. 



PHYLUM V. CILIATA Perty, 1852. 



The Ciliata are free-living or parasitic Heterokaryota, found 

 principally in water, where they exist upon small animal and 

 vegetal organisms and the debris of decomposing plants and 

 animals. Some of them can live in the alimentary canal of man 

 and animals, obtaining their food from its contents, and increasing 

 to such numbers as to cause irritation of the intestine. 



Their movement is by cilia, but always with one end, the anterior, 

 in front. They turn round when desiring to progress in a different 

 direction. This anterior end may be similar morphologically to 

 the posterior, or may be characterized by being more pointed, by 

 having a mouth, or by peculiar sensory cilia (Hypotricha), or by 

 a peristome of long cilia (Heterotricha). The body, which may be 

 spherical or flattened, is divided into an ectoplasm (the cortex) 

 and endoplasm (the medulla). The ectoplasm may simply be a clear 

 outer layer of the protoplasm, or it may be differentiated into three 

 layers. The first is very thick and very tough; the next, called 

 the alveolar sheath, is marked by vertical parallel lines, which are 

 the contractile myoneme threads; while the innermost layer next 

 to the endoplasm consists of clear transparent ectoplasm. 



The semifluid endoplasm is in constant rotatory motion, con- 

 taining food vacuoles, contractile vacuoles, nuclei, pigment granules, 

 colourless granules, crystalline bodies, and smaller particles. The 

 cytostome or mouth is present in all except the parasitic Opalinae. 

 It is a slit in the cortex at the anterior end of the body, which can 

 be opened for the reception of food, but is usually kept closed. It 

 may be on the surface or may be carried inwards by a funnel-shaped 

 depression in the ectoplasm called the vestibule, which may be 

 lined by cilia specialized for the capture of food. 



A cytopyge, or cell anus, occurs in Nyctotherus, but as a rule no 

 definite opening appears, and the undigested food is simply pushed 

 through the cortex. 



544 



