518 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
posterior yolk-mass. As to the origin of the mass of cells which form 
the endothelium of the heart, the author is unable to say anything de- 
finite, but he is inclined to regard it as derived from the mesoblast. 
Development of Teeth in Bottle-Nose Whale.* — Herr Axel Ohlin 
gives an account of the development of the teeth in Hyperoodon rostratus. 
A lip-groove was well developed in the upper jaw of all the embryos ; 
in the lower jaw in the oldest only. No Zahucall nor Zahnfurche was dis- 
cernible. The youngest foetus showed a continuous dental ridge, with a 
few incipient rudiments. The ridge is divided by connective tissue into 
isolated epithelial masses. To its labial side appear on each side 
40 
— cap-shaped tooth-rudiments, which are subsequently reduced in num- 
ob 
her, only 6-7 attaining development. All the enamel germs arise on the 
lateral wall of the dental ridge ; pigment is everywhere distributed; no 
rudiments of replacement teeth were seen. The first two pairs of rudi- 
ments, especially the foremost in the lower jaw, develop more rapidly 
than the others. There is no production of enamel, nor differentiation 
into enamel pulp and enamel epithelium. Besides the lateral dental 
ridges, there are two median epithelial folds in the lower jaw, which 
extend backwards to the most anterior tooth-rudiments, and may possibly 
hint at another generation of teeth. 
Double Gastrula in Lizard.f — Hr. Fr. Kopsch describes the ab- 
normal occurrence of a double gastrular invagination on the blastoderm 
of Lacerta agilis, and discusses the theoretical interpretation of the 
case. There were two distinct embryonic rudiments converging pos- 
teriorly, a convergence which the author regards as due to the median- 
ward cell-movements associated with invagination. 
b. Histology. 
Structure of Striped Muscular Fibre.J — Prof. W. Butherford re- 
turns to a subject to which he has previously made important contribu- 
tions. After a brief historical introduction, he gives an account of his 
methods, and then considers in detail the muscle of the crab in its 
uncontracted and contracted state. He distinguishes (a) the broad dim 
stripe, consisting of Bowman’s elements and including Hensen’s line ; 
(6) the clear stripe proper, consisting of the clear segments proper ; 
and (c) the intermediate stripe, including Hobie’s line and Flogel’s lines. 
A useful synonymy of the complex nomenclature is given. The author 
discusses the theory of contraction, but leaves it an open question. 
“ The appearances of striped muscle that have proved so puzzling 
to the microscopist depend (1) on the fact that the segments of the 
fibrils are not of uniform calibre ; (2) their highly retractile chromatin 
is not equally distributed in the relaxed, and still less so in the con- 
tracted fibrils; (3) when the light is transmitted through the mass of 
fibrils that constitute a fibre, the effects of curvature and of unequally 
distributed chromatin are still more complicated by the superposition 
of many bundles of fibrils ; it is easy to understand why observers 
* Bihang K. Svenska Vetensk.-Akad. Handlingar, xxii. (1897) No. 4, 31 pp. 
and 1 pi. f SB. Preuss. Akad. Wiss., 1897, pp. 646-50 (1 pi.). 
X Journ. Anat- Physiol., xxxi. (1897) pp. 309-42 (3 pis. and 2 figs.). 
