Page:The Eurypterida of New York Volume 1.pdf/150

 Embryology] and one of Brauer's figures. Study of these shows that the carapaces of the larval eurypterids have a closer agreement with Limulus than with the scorpions. In the scorpion embryo and larvae the carapace is relatively of larger size than in the eurypterids, being nearly half the length of the embryo, but it is long and slender, instead of short and broad or semicircular as in the merostomes; the procephalic region early, exhibits a deep frontal emargination and, according to Metschnikoff, a distinct bilobation, features that are found in neither Limulus nor the eurypterids, but which are characters of the adult scorpion. Likewise the development of the cephalothoracic appendages, while homologous in number and original position as to the stomodaeum (embryonic mouth) to that of the merostomes, differs from that of the eurypterids and Limulus in the early development of the pedipalps of the second segment, corresponding to their prominence in the adult scorpion. They are even recognizable earlier than the chelicerae of the first segment, while the following four pairs of walking legs are of uniform size and character.

The homology of the appendages of the cephalothorax repeats itself in the abdomen; here again the number is absolutely in agreement