544 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Prof. Poulton is led to believe tliat both feathers and hairs were, so 
far as their essential structure is concerned, existent in the Reptilian 
ancestors of Birds and Mammals. He gives a representation of a scale 
which contains everything essential to the structure of both hair and 
feather ; on his hypothesis the hair represents the axial, and its inner 
root-sheath the appendicular part of a feather, and this gives an intel- 
ligible morphological significance to the mysterious inner root-sheath, 
which, owing to the mode of its development, is buried deeply beneath 
the surface. 
The author believes that the invaginated inner root-sheath has an 
important function in retaining the hair in its follicle, for it presses 
tightly between the hair and the outer sheath, and with its innermost 
cells imbricated downwards and interlocking with the cuticular cells 
of the hair which are imbricated upwards it gives to the hair a swollen 
base which prevents it from being drawn with ease through the narrow 
neck of the follicle. 
It is claimed that the views expressed in this essay suggest a simple 
and probable morphological explanation of every structure in the hair or 
associated with it. While the dermal papilla, epidermic bulb, medulla, 
hair-shaft, and inner root -sheath all follow naturally from the invagination 
of the suggested proto-mammalian scale, the outer root-sheath is clearly 
the wall of the pit into which the invagination took place. 
Relations of Notochord and Hypophysis in Birds.* — M. G. Saint- 
Remy finds that the notochord is for a certain time fused with the 
hypophysis cerebri in birds, and this union is secondary and caused by 
the growth of the hypophysial invagination. The destruction of the 
end of the notochord is effected by the transformation of its elements 
into embryonic connective cells, which become lost in the surrounding 
connective tissue. 
Formation of Somatopleure and Vessels in the Chick, f — Herr 0. 
Drasch has combined the study of sections at right angles to the blas- 
toderm with the study of “ delaminated ” or flat preparations. After 
fixing, he peeled off the ectoderm, and even the mesoderm from the 
endoderm. He finds that the vascular islands occur only in the middle 
germinal layer, and are formed exclusively from its cells; that the 
somatopleure is altogether epigenetic in its formation ; and that the 
origin of the endothelial vascular wall goes hand in hand with the 
formation of the somatopleure. 
Ectodermic Differentiation in Necturus. { — Miss J. B. Platt has 
studied the ontogenetic differentiation of the ectoderm in Necturus. The 
“ mesoderm ” in the head is differentiated by the yolk spherules which 
it contains into two sharply separable tissues — mesectoderm and inesen- 
doderm.” 
The direct emigration of cells from the single-layered ectoderm leads 
to the formation of a two-layered ectoderm, and ectoderm cells wander 
into the cerebral ganglia and into the nerves of the lateral organs. A 
deepening on the floor of the neural plate touches the wall of the arch- 
* Comptes Eendus, cxviii. (1894) pp. 1283-5. 
+ Anat. Anzeig., ix. (1894) pp. 5G7-70 (] fig.). 
J Arch. f. Mikr. Anat., xliii. (1894) pp. 911-66 (6 pis.). 
