20 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
suggestion on the subject.* Whatever was the first origin of the eyes of 
Vertebrates it is clear that they were of myelonic origin and much more 
deeply placed than at present in adult Vertebrates, and the eye would 
not become a cup till the lens was formed. The passage of the nerve- 
fibres over one part of the edge of the area would prevent the growth of 
the edge at that point, and consequently a gap would be left ; this gap 
is the choroidal fissure, which was probably permanently open during 
a certain stage in the evolution of the Vertebrate eye, and which has 
only secondarily been used as a means of ingress for the mesoblastic 
tissues. 
Origin of Vascular Germs in the Chick.f — M. L. Vialleton brings 
evidence to show that the vascular germs of the Chick arise in the para- 
blast, independently of the mesoderm. To the objection that there may 
have been migration he answers that if the germs could thus migrate 
they would often be found outside the terminal sinus, whereas this is 
very rare, and he has only seen it once. Further, the migration of a 
relatively large mass in a plasmodium would not be easy ; if it is sug- 
gested that it was not effected across the parablast, but between it and the 
ectoderm, an explanation would have to be given of the spherical form 
of the germ. On the whole, then, the author is in favour of the para- 
blastic origin of the vascular germs, and he hopes that the presence of 
these germs outside the vascular area will do something to resolve the 
difficult question of their origin. 
Axial and Lateral Metamerism of the Head in Embryos of Birds.if 
— Herr N. Goronowitsch finds in bird embryos with six metameres the 
first rudiments of the so-called “ ganglionic ridges ” ( Ganglienleisten ). 
They are formed from lateral outgrowths of upright dorsal portions of 
the medullary plate, but perhaps ectoderm apart from the medullary 
plate helps. The ganglionic ridges are most marked in embryos with 
eight metameres, and in this (primary) state they belong to the region 
of thalamencephalon and mesencephalon. In embryos with nine meta- 
meres the ridges have begun to divide up into isolated cells. These 
become identified with cells of the axial mesoderm. They have nothing 
to do w T ith the development of nerves or ganglia. 
The author proceeds to describe the origin of the secondary and 
tertiary ridges, which belong to the posterior region of the medulla 
oblongata. They are much weaker than the primary ridges. The fact 
that ectoderm shares in forming the mesoderm is emphasized. It has 
been believed that a dorsal outgrowth of the brain extends laterally 
from the axial mesoderm, reaches the ectoderm, and fuses with it 
(branchial sense-organs), but the outgrowth is genetically complex. 
The dorsal portion is formed from ectoderm and from the medullary 
plate, the middle part is a differentiation of axial mesoderm, the distal 
part is formed from the middle plate of mesoderm and from the mesoderm 
of ectodermic origin. The development of the tertiary ridges also shows 
that the lateral metameres are formed dorsally from the elements of the 
ridges, and distally from the elements of the axial mesoderm. 
The development of the trigeminus and its ganglion occurs without 
* See this Journal, 1892, pp. 775 and 6. 
f Anat. Anzeig., vii. (1892) pp. 624-7. % Tom. cit., pp. 454-64. 
