572 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
pheral nervous system in Selachians, publishes an elaborate memoir on 
this subject. His general conclusions are as follows. During develop- 
ment the paired fins undergo very distinct changes of position, but these 
changes are by no means identical in all forms. Expressed in the most 
general form, it may be said that the oldest and best defined tendency is 
for the anterior fins to move towards the head, and the posterior towards 
the tail ; but in certain families both tendencies may be reversed. In 
some cases, indeed, two opposite tendencies may be displayed at different 
periods in the development of the same individual. The development 
yields no proof of the lateral fold hypothesis or the concentration theory. 
In origin the muscle primordia show a very striking independence of the 
skeletal primordia, the metamerism of the one having no relation to 
that of the other. The author considers that this shows that the skeleton 
of the extremities must have quite another origin than their musculature. 
He believes that the suggestion which best fits the facts is that the 
skeleton of the paired limbs originated from the elements of the 
branchial skeleton (Gegenbaur). This would explain the discordance 
between the development of musculature and skeleton, and the change 
of position of the limbs during development which is most marked in 
the lowest fishes, and which occurs in a region of the body into which 
gill-arches must formerly have extended. The result of the research is, 
therefore, to add embryological confirmation to a hypothesis hitherto 
supported only by reasoning derived from comparative anatomy. 
Development of Carapace in Chelonia.* — Herr A. Goette has in- 
vestigated this point in Ghelone imbricata and various other tortoises 
(Podocnemis, Emydura , Clemmys ). He has studied especially the de- 
velopment of the costal and neural plates, in order to settle the vexed 
question as to their origin. He finds that in Chelone these bones contain 
no trace of a dermal element. The costal plates are greatly thick- 
ened periosteal ossifications of the cartilaginous ribs, together with an 
ossification in the atrophied dorsal muscles. The neural plates are also 
subcutaneous ossifications, partly periosteal and partly ligamentous in 
origin. Eecently Gegenbaur has revived the old hypothesis of the origin 
of the carapace from a union of cutaneous and deep-seated elements, on 
account of the conditions which prevail in the Atheca. In these a series 
of dermal ossifications forms a mosaic quite distinct from the internal 
skeleton, and Gegenbaur supposes that in the Thecophora this dermal 
skeleton has fused so completely with the internal skeleton as to be 
apparently lost. Goette, on the other hand, believes that the Thecophora 
were originally furnished with a median dermal skeleton which they have 
lost. He considers that there is no evidence to support Gegenbaur ’s 
view of a fusion of such dermal elements with the neural and costal 
plates. 
Albino Eggs of Amblystoma t — Mr. H. W. Britcher describes the 
development of white eggs of Ambly stoma pundatum L. As the embryos 
took form, and began to twitch their bodies when the jelly was disturbed, 
a slight greyish mottling of the sides of the body was seen, and this 
pigmentation slowly increased as the tadpoles grew. Forms about 
* Zeitschr. f. wias. Zool., lxvi. (1899) pp. 407-34 (3 pis. and 3 figs.). 
f Trans. Amer. Micr. Soc., xx. (1899) pp. 69-72 (1 pi.). 
