20 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
somehow prevented, and that an injurious over-ripeness of both sperma- 
tozoa and ova, but especially of the latter, resulted. 
(2) The influence of cold on the reproductive elements. — Ova of sea- 
urchins can survive a temperature of — 2° or — 3° C., but the changes 
which are associated with fertilization are much modified. Thus the 
vitelline membrane was imperfectly formed or suppressed, according to 
the duration of the refrigeration. The receptive prominence where the 
protoplasm of the ovum usually reacts to the stimulus of the penetrating 
spermatozoon was formed slightly or not at all. At the beginning of re- 
frigeration normal fertilization might be observed, after half an hour 
polyspermy occurred, in the second hour no fertilization. More rapid 
than any other change was the disappearance of the usual radiate figures 
in the protoplasm of the ovum. The author then describes in detail the 
remarkable influences of lowered temperature on segmenting ova. 
(3) Staining living cell-substance with methyl-blue . — Ova of Strongylo- 
centrotus lividus placed for a short time in strong solutions of methyl- 
blue, or for a longer time in weak solutions, take up the pigment 
readily. The more they absorb, the more their future development is 
retarded. When returned to pure sea-water, they retain the colour for 
a while, and the pigment is observed at the bases of the ciliated cells in 
the blastula stage. 
(4) Parthenogenesis of Starfish. — Prof. Hertwig was able to confirm 
GreefF s observation that ova of starfishes might begin to develope with- 
out fertilization. The ova of Asterias glacialis and also of Astropecten 
were sometimes seen to segment, usually in abnormal fashion, without 
any fertilization having occurred. In some cases the blastula stage was 
attained, and these blastula embryos were without any vitelline mem- 
brane, which is only formed when fertilization is effected. Though the 
observations on the formation of polar bodies in these parthenogenetic 
ova were not very conclusive, they seem to indicate that a second nuclear 
division, but no second extrusion takes place, a fact of obvious interest 
in connection with the theories as to the relation between the formation 
of polar bodies and parthenogenetic development. 
Maturation of the Ovum of the Fowl.* — Prof. M. Holl begins his 
account with a description of the ova of the newly hatched chick which 
are not yet inclosed within follicles. He then sketches the origin of the 
tunica adventitia (or vitelline membrane), of the membrana granulosa (or 
follicular epithelium), and of the membrana propria, all of which arise 
from the stroma of the ovary. As maturation proceeds, the nucleus 
undergoes a series of changes : — it seems to move from the centre to the 
surface, thence inwards, and finally once more outwards, with slight 
changes of form meanwhile ; the nuclear membrane disappears ; so does 
the nucleolus ; the chromatin substance, at first a fine network, becomes 
distributed in small granules, but collects again in six chromatin rods, 
whose appearance is probably to be associated with the formation of 
polar bodies. Considerable attention is paid to the remarkable yolk- 
nucleus which lies near the germinal vesicle, and to the peripheral in- 
crease of the yolk. The author then describes the appearance of the 
zona radiata , which he regards as a product of the cells of the membrana 
* SB. K. Akad. Wiss. Wien, xcix. (1890) pp. 309-70 (1 pi.). 
