Page:The Eurypterida of New York Volume 1.pdf/59

 bisegmented structure in the metastoma, indicating that it originated from a paired organ. He considers it homologous to the chilaria of Limulus, a pair of movable sclerites set behind the coxal segments of the last pair of legs [ text fig. 10] and remarks that the metastoma of the eurypterids certainly represents a much higher development of the organ than the chilaria of Limulus. Pocock [ 1901, p. 302] considers the metastoma as the homologue of the sternum of the scorpion but the observations of Kishinouye [1891] upon the embryo of  and those of Brauer [1895] on the embryo of the scorpion demonstrate that it represents the appendages of a distinct suppressed segment. For practical reasons we have not counted this abortive first segment of the preabdomen [see diagram p. 24].

Gaskell, in his lately published The Origin of Vertebrates, in order to derive a vertebrate prosomatic or oral chamber fully separated from the gill chambers, has assumed that the metastoma and the operculum of Eurypterus became fused [op. cit. p. 242 and our text fig. 16]. It is safe for us to say that we have no evidence in the eurypterids of any tendency toward the fusion of these organs and that it seems to us such a procedure