26 THE ANIMAL PARASITES OF MAN 



the superficially situated, viscid, and quite hyaline ECTOSARC or ectoplasm, 

 and the more fluid and always granular ENDOSARC (endoplasm) which is 

 entirely enveloped by the ectoplasm. The two layers have different func- 

 tions, the movements originate from the ectosarc, which also undoubtedly 

 fulfils the functions of breathing, introduction of food and excretion ; the 

 endosarc, which in some forms (Radiolaria] is separated from the ectosarc 

 by a membrane, undertakes the digestion of the food. To this apportion- 

 ment of functions to various layers of plasma is due the development of par- 

 ticular cellular organs, such as the appearance of CILIA (filaments), FLAGELLA 

 (whips), SUCTORIAL TUBULES (in the Suctoria} and the myophanes, contractile 

 parts of the ectosarc in infusoria and gregarines, differentiated by striation 

 In many cases (Flagellata, Ciliata), a place is formed for the ingestion 

 of food (oral part, cytostom) to which, not rarely, there is added a straight 

 or curved opening (cytopharynx), through which the food reaches the 

 endosarc ; the indigestible residue is either cast off through the oral 

 part or excreted by a special anal part (cytopyge). In rare cases, organs 

 sensitive to light, the so-called pigment or optic spots (Euglena), are 

 developed. In the case of infusoria the endosarc circulates slowly, and 

 agglomerations of fluids (FOOD VACUOLES) sometimes appear around each 

 bolus of food ; in these vacuoles the food is digested under the action 

 of certain materials (ferments). Even in the lowest protozoa fluids to be 

 excreted are, as a rule, gathered into one, or, more rarely, several " CON- 

 TRACTILE VACUOLES," which regularly discharge their contents ; this action, 

 however, is to a certain extent governed by the temperature of the sur- 

 rounding medium. In some infusoria a tube-like gap in the plasm is 

 joined to the contractile vacuole which usually occupies a certain position ; 

 this forms a sort of excretory duct, and there are also supply-canals 

 leading to these cellular organs. 



Very frequently various substances are deposited in the endosarc, such 

 as fatty granules, drops of oil, pigment granules, bubbles of gas or crystals. 

 More solid skeletal substances are secreted in or on the ectosarc. To the 

 latter belong the cuticles of the sporozoa and infusoria, the chalky shells 

 containing one or several chambers of the Foraminifera, the siliceous and 

 very ornamental framework of the Radiolaria, and the chitinous integument 

 of many Flagellata, Infusoria, &c. Some forms, such as the Amoebinae, 

 make use of foreign bodies found in their surroundings, such as grains of 

 sand and so on, to build their shelters. 



The FOOD consists of small animal or vegetable organisms and of organic 

 waste ; it is usually introduced in toto into the endosarc. On the other hand, 

 the suctoria extract the substance from their prey by means of their suctorial 

 tubes. Many parasitic species also ingest solid food, others feed themselves 

 by endosmosis. 



In all cases ONE NUCLEUS at least is present. It is true that the exist- 

 ence of non-nucleated protozoa, the M oner a, is still insisted upon, but some 

 of these have already proved to be nucleated, and the presence of nuclei 

 in the others will no doubt be established. Very often the number of 

 nuclei increases considerably, but these multi-nucleated stages are always 

 preceded by mononucleated stages. In the infusoria, in addition to the 

 larger or principal nucleus (macronucleus) there is usually a smaller acces- 

 sory or deputy nucleus (micronucleus). 



