88 Development of the Ovum. By W. H. Dallinger & J. Drysdale- 
ovum ; and it was held by leading embryologists that it was round 
this cell that the true embryo was constituted ; but in wbat manner, 
each observer appears to have determined for himself. The disap- 
pearance of wbat was accepted as the germinal vesicle was generally 
agreed to ; but whether before or after impregnation was never fully 
determined. That it merely retrograded to the centre and deter- 
mined segmentation as the result of fecundation, was held by many; 
while the embryogenic vesicle was said to persist, and from it were 
derived the now celebrated “ globules polaires,” or “ Richtungs- 
blaschen,” which bad been variously called by different writers from 
Carus downwards “ white vesicles,” “ round vesicles,” “ clear glo- 
bules,” and so forth, and which are now thought to enter directly 
into the genital organs of the future being ; Balbiani considering 
them of much importance in the evolution, inasmuch as they are 
found just in the region of the ventral layer of the blastoderm 
where the genital organs appear. 
We have only space for a consideration of one of the instances 
adduced by Butschli of earliest ovum development ; but that may 
suffice to indicate the distinctive nature of his work. We select the 
eggs of Nephelis vulgaris. In their youngest state, the yolk is 
retracted from the delicate membrane, and there is, resting on the 
yolk, a minute mound of spermatozoa. At a little distance from 
this spermatozoal eminence there is an eccentrically placed spindle- 
shaped body, composed of fine longitudinal fibres, which at the 
equator of the spindle are swollen to a thick shining granular zone. 
The yolk mass is depressed at one point, and the spindle has its 
long axis directed to that of the flattened yolk. At the ends of this 
body there are clear homogeneous spots, from which rays go forth 
in all directions through the yolk. This spindle-shaped body 
Butschli affirms to be the true germinal vesicle; and it is this 
which is carried upward to the surface of the yolk, by the elevation 
of the upper set of rays proceeding from the homogeneous spot over 
its upper apex, until eventually this spindle is pushed out of the 
yolk in three segments. In the part first protruded fine granules 
appear, and these retain their connection with the fibres in the part 
still enclosed in the yolk, by fine filaments, which also terminate in 
a zone of granules. This protruded vesicle is the “ Richtungs- 
blaschen ” ; the real place and relation of which, in the subsequent 
development of the egg, is nowhere determined by these researches. 
In the stage of partial protrusion of this vesicle, at about a quadrant 
from the point of its exit, another clear space arises sending 
out its radial rays ; this enlarges, moves to the centre, and the 
germinal vesicle — now the “ Richtungsblaschen ” — is at this time 
quite protruded. At a point in the yolk determined by the point 
of exit of the “ Richtungsblaschen,” two minute nuclei appear, one 
in the upper margin of the clear space, and the other between that 
