68 BIOLOGY OF THE PROTOZOA 



the make-up of the all types of nuclei, occurring in pure form in the 

 nucleoli of tissue cells, but only rarely as such in Protozoa. Al- 

 though rare in tln,is pure form (Reichenow describes it in the nucleus 

 of Hcemogregarina stejjanowi) , it is widely distributed in combination 

 with chromatin, and the majority of endosomes are made up largely 

 of plastin. From such combinations the plastin or the chromatin 

 constituent may be separated out during nuclear division or during 

 certain other phases of cellular activity. Thus Hertwug has shown 

 that the endosome of jidinosjjhoBrmm eichhornii, consisting of 

 chromatin and plastin in rather loose combination, loses its chro- 

 matin which is then distributed over the nuclear reticulum while the 

 erstwhile plastin endosome becomes a true plastin nucleolus with 

 characteristic reticular structure and staining capacity (Fig. 22, c). 

 Plastin, furthermore, appears to be the ground substance by which 

 chromidiosomes are cemented together to form compact chromo- 

 somes during division, or to form a more or less definite mass of 

 cytoplasmic chromidia (see Goldschmidt, 1906, Mastujella mtrea). 

 It also appears to be associated with, and to form the matrix of, 

 kinetic elements or endobasal bodies and selects the acid dyes in 

 differential staining. 



{e) Nuclear Sap or Enchylema.— The more fluid substance of the 

 nucleus appears to differ in no marked degree from the intra-alveolar 

 substances of colloidal nature of the cytoplasm. It is relatively 

 abundant in vesicular but scarce in massive nuclei. 



2. MULTIPLE AND DIMORPHIC NUCLEI. 



While a single nucleus is characteristic of the vast majority of 

 Protozoa, multiple nuclei are not uncommon and may be found in 

 every group. In some forms, as in many Mj'cetozoa, the multi- 

 nucleate condition may be due, not only to repeated nuclear divi- 

 sions, but to the plastogamic union of originally independent cells, 

 the aggregate being called a plasmodium. In other cases, as in 

 Foraminifera, Radiolaria and Myxosporidia, the multiple nuclei 

 are due to the incomplete division of the cell body after the nuclei 

 have divided; or no attempt at all is made by the cell body to 

 divide. Analogous multinucleate stages are frequently found during 

 certain phases of the life history of many types such as the antece- 

 dent stages of sporulation and gamete formation in Rhizopoda and 

 Sporozoa. In still other, and in the typical cases, multiple nuclei 

 are present throughout the entire vegetative life, the number 

 ranging from two to several hundred [e, c/., AcfinosphcBriiim). 

 Characteristic and familiar examples of binucleate cells amongst 

 rhizopods are Arcella vulgaris, Pelomyxa hinudeata, etc.; amongst 

 flagellates, Giardia irttestinalis and other species of the same genus. 



