86 PRACTICAL PAEASITOLOGY 



Class V. Ciliata. 



The " Filamented Infusoria," or Ciliates, are so called on account 

 of the peculiar nature of their organelles of movement. They are to 

 be distinguished from the sub-class Suctoria, which have no practical 

 interest and will not be described here. The motor appendages, or 

 " cilia," are present in very large numbers in the Ciliates, and the 

 method of their arrangement is used as a basis for classification. In 

 addition to their locomotor function, they serve also as organelles of 

 nutrition and, like the whips of the Flagellates, they are attached to 

 the ectoplasm by means of basal structures. The superficial layer 

 of the ectoplasm is hardened to form a definite cortex or pellicle, 

 which assures to the parasite constancy of form. As a rule, food is 

 ingested by the agency of a special oral part (cytostome), from which 

 a canal of varying length (cytopharynx) leads into the endoplasm. 

 A special anal part (cytopyge) is frequently present, by means of 

 which undigested food remnants are excreted by the organism. As 

 a rule, one or more contractile vacuoles are present, and, unlike the 

 other classes of the Protozoa, they are present in both the parasitic 

 and non-parasitic varieties. The number and position of these con- 

 tractile vacuoles varies in different species, but never in individuals 

 of the same species. The Infusoria, both Ciliates and Suctoria, are 

 characterized by the possession of two nuclei, which differ in shape 

 and in function. The larger is known as the macronucleus, and the 

 smaller as the micronucleus. The latter is the sex nucleus, and plays 

 an important part in the process of reproduction (see text-books of 

 Zoology). Only one nucleus of each kind is present, as a rule, though 

 this is not invariable. The Opalina are the only members of the 

 Ciliate class which do not present this nuclear dimorphism. The 

 Ciliates almost invariably multiply by simple binary fission, though 

 Ichthyophthirius (seep. 91) is an exception to this rule. The organism 

 encysts as a protective measure in case of dryness or other unfavour- 

 able external condition, and it is probable that, in the case of the para- 

 sitic varieties, infection is conveyed at this stage of their development. 



The Ciliates vary very much in general form. To obtain an 

 adequate idea of their extreme diversity, : the student should extend 

 his observations to the non-parasitic varieties. Free-living Ciliates 

 are to be found in every pond, and abundant material may be obtained 

 by pouring water over a little fresh hay and allowing the infusion to 

 stand for one to three weeks. The extreme motility of the organisms 

 may be reduced by adding a small quantity of carragheen to the 

 water, when they may be examined singly with the aid of a strong 

 lens. Both the arrangement and the movements of the cilia should 

 be observed, as well as the regular pulsation of the contractile 



