672 GEOFFREY LAPAGE 



however, very variable and, under certain chemical and 

 physical conditions, star-shaped and other forms occur. 



The nucleus is vesicular, with a well-marked endosome, 

 which stains deeply and shows, in preparations which have 

 been suitably differentiated, a well-marked meshwork structure 

 (PI. 28, fig. 1). This endosome is surrounded by a clear halo 

 in which no structure can be made out, and this clear area does 

 not appear to be separated from the endoplasm of the amoeba 

 by a definite nuclear membrane. The area of endoplasm 

 immediately surrounding the nucleus stains, however, more 

 deeply than the rest of the endoplasm, an effect which is due 

 to the heaping up, as it were, in this region, of the fine granules 

 of deeply-staining matter which are distributed throughout 

 the endoplasm on the strands of its meshwork. 



The size of the amoeba varies considerably. Doflein (9) 

 gives the size of the motile creeping forms as being 220-250 n 

 long by 40-60 ii broad, whilst the star-shaped forms measured 

 from 60-150 y^, according to the length of their pseudopodia. 

 He says that the nucleus varies from 10-15/^ in diameter and 

 the endosome from 7-10 /^. The amoebae in my cultures were 

 rather smaller than this, the motile forms reaching 200 [i long 

 and sometimes rather longer, when the pseudopodia were well 

 extended ; but the majority of both motile and star-shaped 

 forms varied between 60-100 /^ in diameter. The nucleus 

 measured from 7-9 fi in diameter and the endosome from 

 4-7 A*. It should be mentioned, however, that these measure- 

 ments were made upon stained preparations in which some 

 shrinkage may have occurred. 



The endoplasm usually contains numerous vacuoles as well 

 as abundant granules. One or more contractile vacuoles are 

 present. Penard (21) states that generally there is only one, 

 but that two or three are often present, one of which seems to 

 be the principal one, and that there is almost always a great 

 number of vacuoles distributed here and there, which appear 

 and disappear as if they played the part of contractile vacuoles. 

 I have also found that the presence of several contractile 

 vacuoles is a frequent feature of the amoebae in cultures, but 



