SUMMARY OF CURRENT RESEARCHES. 
189 
experiments on artificial fertilisation. Ova and sperms were artificially 
placed in the oviduct ; but out of 88 cases only 28 were in tlie least suc- 
cessful. The susceptibility to fertilisation seems to depend on invisible 
changes in the vitellus and zona pellucida. Ova in which the ger- 
minal vesicle is still visible are not fertilisable. In no case was more 
than one polar body seen. The movement of the ova through the tubes 
takes 22-47 hours. As many as 20 spermatozoa may be found asso- 
ciated with one ovum. The actual penetration of the ovum by a sperma- 
tozoon was observed. An albuminoid sheath is formed around the ovum 
only when the rabbit is in heat or in natural pregnancy. 
Egg-laying* in Eana fusca.* — Prof. M. Nussbaum adds to a pre- 
viously reported communication a note to the effect that isolated females 
of Hana fusca produce spawn apart from the presence of males. Even 
with the presence of males the edible frogs do not spawn in captivity ; 
both sexes become sterile. 
Oogenesis in Annra.f — Herr J. F. Gemmil describes this in Pelo - 
■bates. In the young ovary the primitive germ-cells lie superficially; 
genital strands grow inwards into the internal tissue and form a some- 
what sponge-like structure with wide meshes lined by genital epithelium ; 
the partitions disappear and a single cavity is formed. Thereupon the 
internal germ-cells form nests of cells by mitosis, and a struggle for 
existence occurs in these nests. Some of the cells form the granulosa 
or internal follicle cells, others disintegrate into nutritive material, 
usually only one forms an ovum. If there is abundant space, several 
ova occur in a nest. In the formation of the granulosa some indifferent 
cells of the genital epithelium also take part. The growing ova press 
towards the central cavity and protrude the genital epithelium before 
them as the external follicular envelope. 
Development of Liver and Pancreas.}: — Prof. J. A. Hammar says that 
the divergences in the early development of the liver cannot be spoken 
of as due to the presence of one primary duct or of two. “ Primary 
liver-ducts,” in the usual sense, occur only in birds. The common 
feature is not the development of a duct or of ducts, but the develop- 
ment of a liver-fold or “ liver-prominence ” caudal to the heart, and the 
constriction thereof into a duct running cranialwards. In Amphioxus 
the simplest condition persists throughout life. In other Vertebrates, 
the duct forms the ductus choledochus ; the cranial portion of the liver- 
fold forms the hepatic parenchyma ; a diverticulum of the ventral wall 
of the liver-fold forms the gall-bladder and its duct. The author then 
discusses the various forms of the hepatic parenchyma in Vertebrates. 
In another paper § Hammar denies that there is a double ventral 
rudiment of the pancreas in the rabbit, dog, &c. From its first emer- 
gence the rudiment is a single caudally directed diverticulum of the 
ductus choledochus. 
Development of Thyroid Gland in Man.|| — Herr J. J. Streiff finds 
that the thyroid begins as a branched tubular gland. But the tubules 
* Arch. f. Mikr. Anat., xlviii. (1897) pp. 545-50 (1 pi.). 
f Arch. f. Anat. u. Entwicklgesch . 1890, pp. 230-8 (2 pis.). See Zool. Centralbl., 
iv. (1897) p. 184 . % Anat. Anzeig., xiii. (1897) pp. 233-47 (14 figs.). 
§ Tom. eit., pp. 247-9 (2 figs.). 
j[ Arch. f. Mikr. Anat., xlviii. (1897) pp. 579-86 (1 pi.). 
