Page:The Eurypterida of New York Volume 1.pdf/154

 and any of the other groups of arthropods and they would derive the Arachnida through the Merostomata from primitive crustaceans. Laurie [Recent Additions, etc. p. 117] however, has pointed out that the relationship of the eurypterids to the Crustacea is not so evident, as they show no special points of affinity with any one group. "The absence of that special modification of three pairs of appendages to serve as mouth organs, which is characteristic of all Crustacea except the Ostracoda, indicates that their point of union must have been very low down the crustacean stem, and the very definite number of segments and arrangements of appendages in the Eurypteridae indicates on the other hand that they are removed a considerable distance from any such primitive type." The fixation of the number of segments in the Cambric eurypterid Strabops is significant as indicating that at this early date they were already far removed from the common ancestor with an indefinite number of segments.

As the most primitive and earliest crustaceans, the trilobites, are clearly not ancestrally or otherwise closely related to the eurypterids and the latter even in the Cambric are far removed from any possible synthetic ancestors, it is a fair question whether it is not proper to look for more primitive arthropods than the crustaceans as ancestors of the eurypterids. We have in mind now the investigations of Bernard [1896] who disputes the relationship of the merostomes to the crustaceans on one hand and to the arachnids on the other, and states that "As arthropods, no relation whatever exists between them; as segmented animals, however, they are both derivatives from the chaetopod annelids, but along different and opposite lines of specialization." Bernard derives the Crustacea from a bent carnivorous annelid, a view which Beecher regards as partly verified by his discoveries concerning the ventral anatomy of the trilobites, and it is therefore worthy of consideration in this place. If we consider the absence of anything in the ontogeny of the eurypterids that would suggest a crustacean nauplius stage, the admitted absence of all crustacean features in the adult forms, and the equal absence of all