500 FOOT. (VOL. XV). 
as traced in fixed material. Its relatively rapid change of 
position in the egg, its accumulation at all the centers of activ- 
ity, — spindle, cone, and sphere, — its subsequent aggregation 
at the periphery, and its final massing at the poles indicate 
that it is not a mere condensation of the cytoplasmic net- 
work; for the migration of such points of condensation from 
the periphery to the poles would cause a marked disturbance 
of the network. The differentiation of a portion of the archo- 
plasm in both spindle and spheres supports the observations 
of those investigators who have differentiated a specific sub- 
stance in either of these two structures. Strasburger (18), 
Boveri (2), Meves (13-14), George Niessing (16), Carl Niess- 
ing (15), Henneguy (10), and von Klinckowstrém (12). 
Whether the archoplasm can be identified with the “hyalinen 
Grundsubstanz”’ Vejdovsky (19), p. 40, has observed in these 
eggs, Iam unable to determine. Thus far I have been unsuc- 
cessful in attempts to differentiate anything else that suggests 
the substance in question; but this fact can scarcely be 
regarded as evidence of its identity with archoplasm ; neither 
have attempts to differentiate the cell-sap of authors proved 
successful; but I am not at all prepared to say that for this 
reason the archoplasm must be identified with the cell-sap. 
The fate of that portion of the archoplasm which forms the 
polar rings has not yet been ascertained ; neither am I prepared 
at present to discuss the difference in form between the two 
rings, nor the lack of constancy in the form of either ring. At 
the pronuclear stage, — when the two masses are complete, —- 
their position in relation to each other appears to be constant. 
The cleavage-planes, however, stand in no constant relation 
to these structures (the substance is not divided between 
the cells), and even the first cleavage sometimes assigns 
both polar rings to one cell, no part of them being consigned 
to the other. 
Centrosome. — Since expressing the belief that the cleavage 
centrosomes are not derived from the middle-piece of the 
spermatozoon (7), and that the middle-piece (the posterior end 
of the head of the spermatozoon) produces an effect upon the 
cytoplasm comparable to the effect produced on it by the 
