40 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
and axial mesoderm, and there is, therefore, no homologue of the 
“ periaxial Strang.” Wandering cells from the neural crest and ectoderm 
give rise to the cartilage of the head, and may contribute to the 
formation of certain other tissues ; but there does not seem to be any 
evidence that they take part in the formation of the “ cutis.” 
Experimental Studies on Eggs of Teleosteans.* — Prof. T. H. 
Morgan, who has experimented with the pelagic eggs of Ctenolabrus and 
Serranus, and with the large eggs of Fundulus, applied the method of 
Pfliiger, Roux, and others ; he has also tried to test by experiment the 
theory of concrescence of the embryo. After removing one of the first 
two blastomeres, he found that the resulting embryo was larger than half 
the normal embryo, but not so large as the whole. In the egg operated 
on there remains half the segmentation-nucleus, more than half of the 
protoplasm, and all the yolk ; there results an embryo of nearly two- 
thirds the size of the normal. The author thinks the conclusion seems 
to follow that the size of the embryo is determined by the amount of 
protoplasm present, and not by the quantity of nuclear matter. If the 
first cleavage results in unequal blastomeres, the embryo is smaller when 
the smaller half is left, and larger when the larger remains. 
From experiments made by removing the yolk we find, to state 
matters generally, that the egg of Fundulus is able to adapt itself to 
most unusual conditions, and still produce an embryo that is distinctly 
that of Fundulus. The author suggests that this points to the conclusion 
that, while the egg during development adapts itself to the necessities of 
the occasion, by utilizing the mechanical means placed at its disposal, 
it is a mistake to suppose that the external conditions determine the 
series of phenomena, for the same result follows even when the primary 
conditions are very much altered. 
In the study of concrescence two points had to be tested — is the 
head a fixed point, and does the substance of the germ-ring go to make 
up the embryo ? He finds that the embryo, ciit off from all connection 
with the germ-ring on one side, elongates backwards and produces an 
embryo in which the right and left sides are alike and equal. From 
this he concludes that, in the elongation of the embryonic knob back- 
wards, the head remains a fixed point, and the elongation is due to an 
extension backwards of the mass ; the germ-ring takes no important 
part in the formation of the embryo. 
Growth of Blastoderm in Teleosteans.f — MM. R. Koehler and E. 
Bataillon have studied on eggs of Leuciscus jaculus the vexed question 
of the mode of growth of the blastoderm. Their observations lead them 
to support the views of Kuppfer, for they find that the opaque region 
remains fixed at the germinal pole, while the blastoderm extends 
regularly over the vitellus ; as it does it describes circles which are 
more or less exactly parallel to the equator of the egg. When the 
blastoderm covers half the egg the first rudiment of the embryo is 
differentiated in the form of a small shield on its thickened edge. 
While the blastoderm continues i^s development the embryonic rudiment 
elongates ; when the yolk is almost entirely covered with the blastoderm, 
* Anat. Anzeig., viii. (1893) pp. 803-14. 
t Coinptes Rendus, cxvii. (1893) pp. 490-3. 
