NUCLEI AND KINETIC ELEMENTS 59 



dissolved in strong acids, dilute alkalies, calcium carbonate and 

 sodium phosphate some of which have no apparent effect on nucleoli 

 which remain undissolved in potassium hydrate or in a 1 to 3 per 

 cent acetic acid (Doflein). 



That there is a great difference, however, in the ultimate chemical 

 composition of the nuclear structures which we call chromatin is 

 apparent, as Minchin clearly points out, from the diversity of forms 

 of life, although the chromatin contained in them appears to be the 

 same. If chromatin is the seat of factors ha^'ing to do with definite 

 adult structures it follows that chromatin in different organisms 

 must be different in ultimate composition. Or, to state it in another 

 way, the differences between Amceha, sea-urchin and mammal are 

 relatively no greater than the differences between Amoeba, the egg 

 of a sea-urchin and the egg of a mammal, nor are these relatively 

 greater than the differences between the chromatin of Amceha, of 

 the sea-urchin and of the mammal. Chromatin in these three cases 

 represents the last stage of evolution in each no less surely than the 

 adidt structures do, hut they are l)eyond reach with our present 

 means of analysis. 



In vesicular nuclei the chromatin granules may be distributed 

 more or less evenly throughout the nucleus, or they may be segre- 

 gated in "net-knots" or either alone or combined with other nuclear 

 substances in one large central globular mass to which Minchin 

 gives the name endosome as an equivalent for the term Binnen- 

 korper, or they may be aggregated in several such globular masses 

 or multiple endosomes distributed throughout the nucleus or plas- 

 tered to the nuclear membrane. 



Endosomes maA' consist entirely of chromatin as appears to be 

 the case in nuclei of some Microsporidia (Glugea and Thelohania), 

 or some flagellates {Proicazekia, Belar, 1920, etc.), or in the multi- 

 ple endosomes of Noctiluca iniliaris or of Polystomella crwpa. Or 

 they may be composed of chromatin and plastin in various com- 

 binations. Thus in AciinosphcBrivm eichliornii in some stages of 

 nuclear activity, the chromatin component is in the form of an 

 incomplete ring which partially encloses the plastin portion (Fig. 

 22, c). In other cases the plastin is entirely surrounded by a cortex 

 of chromatin which may be dense and compact as in the case of 

 many types of rhizopods and Sporozoa or loosely aggregated as in 

 nuclei of Endamoeha intestinalis (Fig. 23). The distributed gran- 

 ules of deeply staining material which represent the substitute for 

 a nucleus in Dileptvs a user are similarly composed of a plastin 

 core and a chromatin cortex, the former increasing enormously 

 after treatment of the animal with certain kinds of food such as 

 beef broth. Here the term endosome is scarcely applicable since 

 the bodies in question are not inside a nuclear membrane, but they 

 appear to be morphologically equivalent to these intranuclear 



