222 
KICHAKD ASSHETOX. 
In the hopeful expectancy of sucli a chapter I venture, as 
one who has taken a practical part, though but a small part, 
in the attack upon the problems in question, and as one who 
appreciates to the utmost the magnitude and inspiring in- 
fluence of the Professor’s work, to urge the force of certain 
objections which appear to me as formidable obstacles to the 
acceptance of some of Hubrecht’s vieAvs. 
Chaptek I. 
'J’he Ei'thekian Blastocyst. 
Beginning with the question of the segmentation of the 
ovum of Eutherian mammals, and passing rapidly over 
the manner in which the morula stage is produced, Hubrecht 
describes the embryo of this stage as consisting of an inner 
mass of cells which he calls the embryonic knob, and an 
outer layer called the trophoblast, and gives three figures 
(2, 3, 6, p. 7) in which the inner cells (the embryonic knob) 
are shown to exhibit “a different reaction against staining 
reagents than the peripheral” (p. 6), the inner cells being 
lighter in colour than those of the outer layer. 
Perhaps the gist of the whole paper is foreshadowed in 
the second paragraph of Chapter I, p. 3, where the author 
speaks of “the erroneous conclusion that the mammalian 
blastocyst was derived from the Sain-opsidan by a process 
consisting in the gradual disappearance of the yolk, with 
retention of the other developmental characters.” 
It is upon the establishment of the erroneous nature of 
this conclusion that the greater part of the rest of Hubrecht’s 
conclusions must be based. 
It seems to me, therefore, to be of the greatest importance 
to weigh with care the evidence of the manner in which this 
morula stage of the mammalian segmented egg is attained, and 
to consider other views which have been advanced, whether 
from actual observation or as the outcome of reflection. 
This part of the development of the mammal Hubrecht 
treats very cursorily. 
