102 A Sketch of Comparative Embryology. [| February, 
satisfactory observations of the polar globules of the eggs of any 
of the Rotifera or Arthropoda have yet been made; but, as the 
interest in this subject is very recent, the globules may yet be 
found in those classes. 
When the polar globules ave formed, the following events may 
be assumed probably to occur. Ed. van Beneden’s account of 
the development of the polar globules in the rabbit may be espe- 
cially mentioned as exceptional. The history as here given is 
based upon observations made upon a limited number of inverte- 
brates. When the nucleus disappears it is replaced by a spindle- 
shaped body known as the hern-spindel or Anglice nuclear spindle, 
which is generally regarded as the metamorphosed nucleus. It 
consists (Fig. 4) of a small number of fine, parallel threads, which, 
converging towards either end, run out into two points. The 
fibres are all thickened in the middle at the same level; these 
thickenings produce the appearance of a distinct plate or disk in 
the middle (Strassburger’s Kernplatte). It will be convenient to 
adhere to the term nuclear plate to designate these thickenings. 
The spindle lies perpendicular to the surface of the egg. The 
pointed end of each spindle occupies the center of a clear space, 
from around which radiate fine threads, thus 
producing a sun-like figure. The whole 
spindle, with the two suns, has been named 
the amphiaster. 
The character of the next series of 
changes is shown in Fig. 5. The spindle 
is partly excluded from the egg, one end 
3 projecting outwards and enclosed by a dis- _ 
Fic. 4—Ovarian egg of tinct mass of protoplasm, constricted around — 
Haemopis, aia lade pa the base. The “kernplatte” has divided in 
duncle attaching the egg to two, one-half moved towards either end of 
the spindle. The spindle next divides and 
the inner moiety retreats into the egg, the outer into the protuber- 
ance, which thus becomes the first polar globule. The part of 
the spindle within the egg, transforms itself into a second spin- 
dle, which develops a second globule like the first. Frequently 
a third globule is also formed. The connection of the globules _ 
with the yolk lasts some time, and in the case of leeches isnot 
dissolved until segmentation begins. These globules take no part _ 
in the further history of the egg: they sen ht is not 
