ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
569 
Manner calls this stage the new segmentation of the skeletogenous 
tissue. The history of the two sclerotome halves is then traced in 
the different forms studied. 
Development of Bat.* — Herr 0. van der Stricht publishes a pre- 
liminary note on his researches on the fixation of the egg in the uterus 
in Vespertilio noctula. As in the hedgehog, the first stage in fixation 
is the formation of a connection between the primitive outer layer 
(placental ectoblast or trophoblast) and the wall of the uterus. This 
is accompanied by a desquamation and absorption of the epithelium 
of the uterus at the area of fixation. In the second phase of fixation 
the trophoblast proliferates greatly in an area corresponding with the 
future placenta. At this stage it is possible to distinguish between the 
embryonic placental region and the extraembryonic placental region. 
The third stage is signalised by the disappearance of the sharp line of 
demarcation between maternal and foetal tissues. This is due to the 
development of a mass of vascular epitheloid tissue which arises from 
the primitive outer layer and penetrates the uterine wall. During this 
stage the amniotic cavity appears, but it is not until the next stage 
that it becomes a distinct space separating the embryonic disc from the 
placental region. In this next stage the amniotic folds appear, being 
formed from the embryonic ectoblast and the adjacent mesoblast. The 
placental ectoblast (cytoblast) takes no part in their formation. 
Segments of the Vertebrate Head.f— Dr. Charles Hill finds that 
in Teleostean and chick embryos at a very early stage the whole neural 
tube, including the brain, is distinctly segmented. In the chick the 
segmentation soon disappears in fore- and mid-brain, but persists for 
a longer period in the medulla. So transient is the primary segmenta- 
tion of the anterior part of the brain, that the supervening secondary 
segmentation has previously been homologised with the persistent 
primary segments of the medulla. In the primary segmentation there 
are three divisions to the fore-brain, two to the mid-brain, and six in 
all to the hind-brain. Of these six, the first forms the cerebellum, and 
the remaining five represent the medulla. The Vertebrate head has, 
therefore, primarily eleven segments. The paper is a preliminary com- 
munication only, and is illustrated by some remarkable figures, which 
display the segmentation of the brain in living trout embryos. 
Visceral Clefts of Echidna. t — Herr Maurer has had an opportunity 
of examining Semon’s sections of Echidna embryos, and publishes a 
preliminary account of his observations on the organs which originate 
from the visceral clefts. These organs fall into two sets: — First, 
those which exist also in forms with open gill-clefts (Fishes and larval 
Amphibians). These are the thyroid, thymus, and post-branchial 
bodies. Second, those which originate from the degenerating clefts, 
and therefore appear in Amphibians at the time of the metamorphosis. 
These are the epithelial bodies, best represented by the carotid gland. 
In Echidna there are four gill-clefts, of which the first three form for 
a time open clefts. The first becomes specially modified in connection 
* Anat. Anzeig. (Erg'anzungaheft), xvi. (1899) pp. 76-88 (7 figs.). 
t Op. cit., xvi. (1899), pp. 353-69 (22 figs.). 
j Tom. cit. (Erganzungsheft), xvi. (1899) pp. 88-101 (10 figs.). 
