ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
587 
protovertebral ridge was split into a ventral and a dorsal limb both 
segmented, a fact hitherto unnoticed in the development of mammals. 
In front of the eight cervical segments there were three distinct segments 
on the dorsal limb above mentioned. The relation of the double 
metameric ridge to the musculature of the neck is then briefly discussed, 
and a full description is promised. 
Surface Views of Frog Embryos.* — Herr F. Ziegler in endeavour- 
ing to construct correct models of the embryos of Bana temporaria when 
the blastopore is closing and the neurenteric canal being formed, has 
observed the surface appearance of living embryos. Of this he gives a 
number of figures, to a description of which his communication is 
devoted. 
Alleged Parthenogenesis of Frog Ova.| — Hr. H. Dehner gives an 
account of alleged cases of parthenogenetic segmentation in Vertebrate 
animals and communicates the results of his own observations on Band 
fusca. With all possible precautions he removed ova from a female frog 
taken from the sexual embrace, placed them in water, and examined 
them after 24 to 48 hours. About 1500 ova were thus examined. In 
one hundred of these unfertilized eggs three showed irregular segmenta- 
tion furrows. The groove-like insinking of the surface, the occurrence 
of partial constrictions of more or less spherical form, the limitation of 
these changes to the clear pole of the ovum, and the behaviour of the 
pigmentation were strikingly suggestive of what occurs in the normal 
segmentation of a fertilized egg. 
Segmentation of Cephalic Mesoderm in Pelobates fuscus.if — Mr. A. 
N. Sewertzoff finds that there are, in the head of Pelobates fuscus , three 
pairs of mesodermal segments, each of which corresponds to a body- 
segment. The external segments of Gotte are not mesodermal in origin, 
but are ectodermal structures and have no relation to segmentation. In 
other words, the segmentation of the head of anurous Amphibians 
belongs to the type commonly found in lower Vertebrates. 
Development of Elasmobranchs.§ — In the present set of “ notes ” 
Mr. A. Sedgwick deals with (1) the formation and growth of the embryo, 
and the blastopore ; (2) the formation of the mouth and gill-clefts ; and 
(3) the segmentation of the cephalic mesoderm and the development of 
nerves. He finds that, immediately before closing, the blastopore of 
Elasmobranchs is an elongated narrow slit, slightly dilated in front and 
more dilated behind. Between these two points it takes the course of a 
reversed letter S. The anterior part perforates the floor of the 
medullary canal and is dorsal ; this is continuous round the end of the 
tail with a ventral part, which extends forward along the ventral side of 
the tail, as far as the yolk-stalk, along which it passes to continue back- 
wards along the yolk. The behaviour of the blastopore of Elasmo- 
branchs, in its relation to the anus, neurenteric canal, and growing 
point, very closely resembles that of the Frog as described by Assheton 
and Robinson. 
* Auat. Anzeig , vii. (1892) pp. 211-5 (3 figs.). 
f Verh. Physik. Med. Gesell. Wurzburg (Semper), xxvi. (1892) pp. 1-18 (1 pi.). 
i Bull. Soc. Imp. St. Petersburg, 1892, pp. 99-103 (1 fig.) 
§ Quart. Journ, Micr. Sci., xxxiii. (1892) pp. 559-86 (1 pi.). 
