ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
21 
any help from the so-called ganglionic ridge. In the development of a 
nerve two facts must be clearly distinguished : the development of tho 
tract of nerve-carrying tissue (which in the case of the bird’s trigeminus 
is purely mesodermic), and the proper development of the nerve which 
begins with the appearance of the neuroblasts. The author’s views 
may be generally expressed as a combination of those of Goette with 
those of His. 
Maturation of Amphibian Ova and Fertilization of Immature Ova 
of Triton.* * * § — Prof. G. Born has extended O. Schultze’s observations on 
the maturation of Amphibian ova. He chiefly studied Triton tseniatus. 
He finds that the peculiar coil of transverse threads in the ripening 
ovum arises directly from the chromatin framework, and describes the 
transformation in detail. This is difficult to follow without figures, 
which will be published in a future memoir. 
In the ripest ovarian ova the nuclear spindle of the first polar body 
was almost complete ; in the ova from the visceral cavity the spindle 
lay tangentially under the surface, and the chromosomata were dividing 
into loops ; in the oviducal ova with firm spherical envelopes the first 
polar body had been extruded ; in the uterine ova the second spindle 
was complete. The author proves that all the oviducal ova and even 
those from the visceral cavity are, under certain conditions, capable of 
being fertilized and of development. From a few of the visceral ova 
Born reared morulsB, from distal oviducal ova normal larvae. 
Fertilization of Axolotl Ovum.f — Herr R. Fick finds that the 
middle portion of the spermatozoon gives rise to an attraction-sphere. No 
attraction-sphere was observed in association with the female pronucleus, 
but the two attraction-spheres of the first segmentation spindle seem to 
arise from the division of that associated with the spermatozoon. Some- 
times as many as nine spermatozoa were found in the ovum. 
Development of Endothelium of Heart of Amphibia.^ — M. V. 
Roudnev has chiefly studied embryos of Bana temjporaria. He finds 
that, in the region of the pharynx, the endoderm forms a layer made up of 
cylindrical cells, which do not take any part in the formation of the heart. 
The vitelline mass, which has the character of a primitive endoderm, 
and which gives off whole layers in the region of the heart, at first 
nourishes the embryo directly, and next plays the part of a formative 
element of the blood. In the latter case it is a vitello-vascular layer, 
and it is from this last that there is formed the endothelium of the heart, 
of the veins, and of the aortic arches. The author thinks it is of im- 
portance to distinguish between the paired and unpaired types of 
formation of the Vertebrate heart. 
Multiple and Partial Development in Amphioxus.§ — Mr. E. B. 
Wilson finds that twin and double embryos can be produced in great 
numbers and with perfect ease by shaking apart the blastomeres of the 
two-celled stage. A normal blastula is formed by each, but of half the 
usual size, and so it is also with the gastrula. If the four blastomeres 
* Anat. Anzeig., vii. (1892) pp. 772-81 (1 fig.) and 803-11. 
f Tom. cit., pp. 818-21. 
t Congres Internat. de Zoologie, II. i. (1892) pp. 101-3. 
§ Anat. Anzeig., vii. (1892) pp. 732-40 (11 figs.). 
