570 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
with the ear, and gives rise to no epithelial residue. The second gives 
rise to the carotid gland, but takes no part in the formation of the 
thymus. The third cleft gives rise to a large outgrowth which is the 
primordium of the whole thymus. From this cleft an epithelial body 
also originates. The fourth cleft gives rise to an epithelial body. The 
post-branchial bodies originate as median evaginations of the wall of 
the fourth cleft. The thyroid arises as a median unpaired evagination 
of the ventral floor of the gullet. In other mammals the thyroid arises 
from a fusion of such an unpaired primordium with the post-branchial 
bodies, but in Echidna the three structures remain distinct throughout 
life. Similarly in higher mammals the thymus has usually a more 
complex character arising in connection with two or more clefts. The 
author gives a series of diagrams to illustrate the relation of the con- 
ditions seen in Echidna to those found in the lower Vertebrates. 
Histogenesis of the Mesenchyme.* — Herr A. Spuler has investi- 
gated the development of cartilage and of bone in Mammals, Am- 
phibians, and Selachians. He finds that before the formation of the 
matrix the future cartilage is represented by branched cells whose 
brauches are closely interlaced. Round the network so formed the 
matrix is secreted, and the interlacing fibrils separate from the cells, 
which constitute the capsular cells of the cartilage. In the formation 
of fibres the cells produce fine fibrillse round their periphery ; these 
fibrillae separate from the parent cells, and become covered and largely 
concealed by the secretion of matrix. In the development of bone the 
author considers it as proved that the osteoblasts are united by proto- 
plasmic processes to the osteoblast layer, to each other, and to the 
neighbouring connective-tissue cells. He believes that the cartilage 
cells are directly converted into bone-corpuscles. The matrix of the 
bone arises in connection with the processes both of the osteoblasts 
and of the connective-tissue cells with which the former are connected. 
After the formation of the fibrillar matrix, a lime-containing cement 
substance is a lded to it. The author believes that the latter originates 
from darkly tinged granules found in the osteoblasts and their pro- 
longations. 
Development of Lizard’s Tongue.f — Dr. Franz Bayer gives a short 
summary of his observations on this subject in Lacerta agilis. The first 
indication of the dorsum linguae is a proliferation of the epidermis in a 
median groove between the halves of the first visceral arch. Later this 
groove becomes a ridge, which is divided into first two and then three 
ridges separated by furrows. The tip of the outgrowth divides, and 
forms the future forked tip of the tongue. Of the muscles the hyoglossi 
appear early, and are to be regarded as branches of van Bemmelen’s row 
of cells ; they have no primary connection with the tongue. The 
lingual glands originate on the eighth day by an invagination of the 
epithelium. 
Development of Spleen.J — Dr. W. Tonkoff gives some account of the 
very diverse opinions held by embryologists as to the origin of this 
* Anat. Anzeig. (Erg'anzungsheft), xvi. (1890) pp. 13-6; 
t Morphol. Jahrb., xxvii. (1899) pp. 712-6 (5 figs.). 
X Anat. Anzeig., xvi. (1899) pp. 405-6. 
