DIMASTIGAMCEBA GRUBERI 263 



side of the anterior end can, not infrequently, be made out a slight de- 

 pression, having the appearance of a small cytostome. The two blepharo- 

 plasts, which were first clearly described by Alexeieff (19125f), lie one in 

 front of the other on the surface of the cytoplasm within this depression, 

 and the flagella arising from them pass through the opening of the depres- 

 sion. In many individuals a short fibre can be traced from each blepharo- 

 plast as far as the nucleus, where it ends in a small thickening or elevation 

 of the nuclear membrane. In some forms the nucleus may be near the 

 centre of the body, or even at the posterior end, and in such cases it may 

 or may not be possible to trace fibres from the blepharoplasts to the 

 nucleus. The nucleus has a large central karyosome, which is connected 

 with the nuclear membrane by radiating filaments. On the inner surface 

 of the membrane are granules of chromatin. The nucleus of the amoeboid 

 form is spherical, but in the flagellate phase, in which a connection between 

 the blepharoplasts and nuclear membrane can be made out, the latter 

 structure may be slightly drawn out towards the blepharoplasts. A con- 

 tractile vacuole is present. In the flagellated forms it is behind the nucleus 

 in the thicker portions of the body. The flagellates, which are typically 

 pear-shaped, vary in length from 10 to 30 microns. The relation of the 

 blepharoplasts to the nucleus are of considerable interest, Alexeieff 

 (1912^) stated that when the flagellate phase was to appear, two granules 

 separated from the karyosome and migrated to the surface of the body, 

 retaining in some forms a connection with the karyosome. Wilson (1916) 

 also described the separation from the karyosome of a granule, which 

 migrated into the cytoplasm and became the blepharoplasts. The writer, 

 after examining many thousands of amoebae at all stages of flagellum 

 formation, has failed entirely to trace the origin of the blepharoplasts from 

 the karyosome. Appearances suggestive of such an origin are occasionally 

 seen, but they are too inconstant to justify the conclusions that the 

 blepharoplasts arise in this manner. 



On agar plates there occur amoebse with one, two, or four nuclei 

 (Fig. 61). Those with one nucleus develop, as a rule, a single pair of 

 flagella (Fig. 1 20, 1-7) ; those with two nuclei two pairs (Fig. 120, 13 and 14) ; 

 and those with four nuclei four pairs (Fig. 120, 15). It is evident, therefore, 

 that each nucleus has associated with it a pair of blepharoplasts. If an 

 amoeba has a nucleus in process of division, it will still develop flagella, 

 but in this case two pairs appear, as in the forms with two nuclei (Fig. 120, 

 II and 12). It seems evident that with nuclear division the blepharoplasts 

 have divided. In some cases an amoeba, with a single nucleus showing no 

 sign of division, will develop two pairs of flagella (Fig. 120, 8-10). It 

 would seem justifiable to conclude that the single pair of blepharoplasts 

 has divided preparatory to nuclear division, which has not as yet visibly 



