1887] Embryology. 203 
late, as simple inpushings into a space rich with blood-cor- 
puscles , 
In this connection the reader is referred to this journal, vols. 
xix. p. 560; xx. pp. 666, 825, and 862.— F. S. K. 
Polar Globules in the Crustacea.—The question whether 
tere are polar globules formed in the maturation of the arthro- 
egg has long remained in doubt, and both Minot and Bal- 
se have suggested that their absence was connected with the 
existence of parthenogenesis. Several writers have described 
and figured what might be polar globules, but their observations 
have contained a considerable element of doubt. Recently, 
August Weismann (Zool. Anzeiger, ix. 570-573, 1886) gives a 
preliminary account of the studies in this direction made by 
himself and his pupil, Chiyomatsu Ishikawa, on the partheno- 
genetic eggs of several Crustacea. In Polyphemus oculus, the ripe 
summer egg forms a polar globule in the normal manner, with 
a soen; the long axis of which is at right angles to the 
surface of the egg. Then the egg enters the brood space, and 
there quickly forms a vitelline membrane. While this is going 
on the spindle divides, and the polar globule, which contains 
considerable protoplasm, becomes separated from the egg. This 
takes place at the animal pole of the egg, and then the inner 
end of the spindle becomes converted into the segmentation 
nucleus, and segmentation quickly follows. At the close of the 
second segmentation the polar globule itself divides and then 
quickly disappears; the authors think it is absorbed again by 
the egg. In Bythotrepes longimanus the process is much the 
same, except that the transformation of the proximal end of the 
spindelkern into the segmentation nucleus has not been seen. 
At the eight-cell stage the remnants of the polar globules are 
still visible, sunk between the cells, but with further development 
of the egg ‘they sink deeper and finally disappear. Grobben had 
described polar globules in Motina paradoxa and Weismann con- 
firms the observation, describing the process of formation as 
witnessed in the living egg. It does not differ materially from 
that outlined in the other species. In Leptodora, Weismann 
found a body very like the polar globules of Polyphem mus and 
Bythotrepes, but did not see the method of their formation. In 
Daphnia longispina the spindle is apparently not so evident 
as in other cases, but its place is taken by a clear spot about 
half-way between the pole and the os see Shortly after this 
the polar globule appears on the surface, its ada frequently 
retaining traces of the ieeryokinetic figures of formation while 
its circular or oblong body remains homogeneous. During the 
first and second segmentation of the e “gs the polar globule itself 
divides, the process being accompanied by karyokinesis and the 
resulting cells ASEAN close together. In this species the egg 
