586 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
observations of abnormal frog ova. Tbe abnormalities were produced 
by polyspermy and over-ripeness. First be describes abnormalities of 
segmentation ; secondly, cases in which more or less large parts of the 
yolk remained undivided ; thirdly, disturbances of gastrulation resulting 
in imperfect closure of the blastopore, primitive groove, or “ Urmund,” 
and consequent malformations. The “Urmund” may remain open 
throughout its entire length, or the closure may be partial, or almost 
complete. According to Hertwig the Urmund cleft originally divided 
the central nervous system into two halves of a ring, and this view is 
corroborated by the abnormalities in which closure is inhibited. 
After describing the various malformations to which incomplete 
closure of the Urmund gives rise, Prof. Hertwig discusses similar 
malformations in other Vertebrates — Terata mesodidyma and kata- 
didyma in Teleostei, and Spina bifida in Amniota. 
Prof. Hertwig believes that the original Urmund extended along the 
whole dorsal surface of the embryo. The dorsal groove represents the 
line of union of the Urmund-margins. The middle layer arises in 
reality altogether from a process of coalescence along these margins. It 
is important to notice Hertwig’s statement that “ what we term at 
different stages the Urmund is not one and the same unchanged and 
persistent organ, but rather different areas of an organ which is renewed 
by growth posteriorly as it becomes used up anteriorly by concrescence 
and differentiation.” It is not, however, possible for us to give here a 
just summary of the author’s restatement of the concrescence theory of 
His, or his interpretation of the various forms of Vertebrate gastrulation. 
In a subsequent section the author defends his coelom theory against 
Goette’s critique. He then passes on to show how the Urmund is re- 
lated to malformations of various sorts. The last section is devoted to 
answering the question how in a simple egg multiple rudiments of organs 
may arise. The author concludes that in an over-fertilized (poly- 
spermic) ovum, different factors conflict ; on the one hand, forces tending 
to development and incited by the fertilization, on the other hand, 
influences of an inhibiting and disturbing kind due to the injury which 
the ovum has sustained by overmaturation or other disadvantageous 
conditions operating before fertilization. As the first or the second 
factors predominate the result of development varies. 
Embryos of Apes.* — Prof. J. Kollmann gives a short account of an 
embryo of Cercopithecus cynomolgus from "Sumatra. It measured 9'5 
mm. in length. The back was slightly curved, while the pelvic 
curvature was strong and continued into the tail, which lay bent forward 
as far as the forehead. The strong tail was relatively larger than in the 
adult. After removing the amnion the delicate character of the 
membrana reuniens anterior was noticeable. A comparison with human 
and other mammalian embryos made it likely that the age of this foetus 
was about four weeks. The head was larger than the trunk. Neither 
head nor trunk suggested anything pithecoid. The Wolffian ridge, 
giving origin to the appendages, was sharply defined off from the proto- 
vertebral region, which exhibited eight cervical, twelve thoracic, six 
lumbar, six sacral, and many caudal segments. In the cervical region the 
* Anat. Anzeig., vii. (1892) pp. 335-40. 
