22 . PRACTICAL PABASITOLOGY 



(2) E. histolytica, the dysentery Amoeba of man, occurs in Egypt 

 and Southern and Eastern Asia. It resembles the E. tetragena 

 in having a well-developed ectoplasm, but it is to be distinguished 

 from it and from the other Amoebae which are found in the intestine 

 of man by the structure of the nucleus in the resting stages. The 

 nucleus of E. histolytica has no surrounding membrane and contains 

 very little chromatin ; for this reason it is rarely seen in the living 

 organism. It contains, however, a small caryosome, and in this 

 conforms to the general structural scheme of the amoeboid nucleus. 

 E. histolytica differs from all other parasitic Amoebae in the nature 

 of its permanent stages. Usually the entire amoeboid organism 

 encysts and the shell is readily discoverable among the faeces. In the 

 case of the E. histolytica, however, the cyst is a minute structure 

 sloughed from the surface of the organsim, and is extremely difficult 

 of detection. 



It is evident from the foregoing how important is the part played 

 by nuclear structure in distinguishing the different species of Amoebae, 

 not only from one another, but, what is of even greater importance to 

 the parasitologist, from body-cells such as the leucocytes (fig. 1, e). 

 The student should seek every opportunity of making himself acquainted 

 with the structural details of the Amoebae, and for this purpose the 

 varieties which are indigenous and easily obtainable, furnish excellent 

 material. 



Class II. Neosporidia. 



Although many of the parasitic Protozoa closely resemble certain 

 free-living forms, there are, nevertheless, a large number of varieties 

 which possess no such resemblance. These are usually classed in a 

 special group as Sporozoa. But with a greater knowledge of the 

 subject, it has become increasingly doubtful whether these so-called 

 ''Sporozoa" are possessed of any attribute in common other than 

 their adaptation to parasitism. In all other directions, they differ 

 from one another so markedly that it has been found necessary to 

 divide them into at least two groups. Of these, one, the Telo- 

 sporides, appears to possess a certain distant resemblance to the 

 Flagellates. The other group, named by Schaudinn Neosporides, 

 includes the Microsporides, Myxosporides and Actinomyxides. It 

 approximates more closely to the Amoebina, certain varieties being 

 capable of amoeboid movement. The Neosporides are distinguished 

 by the formation of special reproductive cells (cnidospores), which 

 always possess a hard bi- or tri-valved shell, several (at least four) 

 nuclei, and one to four polar nematocysts. These consist of a 

 vesicular wall or capsule surrounding a cavity filled with fluid, contain- 

 ing a long and usually spirally coiled thread continuous with the wall 



