82
NEW YORK STATE MUSEUM
In summing up the evidence regarding the life mode of the eurypterids, and in view of the variety of forms with incipient adaptations, it would be a legitimate inference that the whole group was not so highly specialized as the recent merostomes and was still able to use different methods of locomotion though no one of them with great proficiency. Some were best adapted to swimming, others to crawling and many to finding their food by grubbing in the mud.[1]
- ↑ In connection with the locomotion of the merostomes, the question suggests itself whether they may not have been in the habit of swimming on their backs; this swimming attitude being assumed by the young of Limulus, and directly asserted for the merostomes by Patten [1890].
The peculiar attitude of the young Limulus has been described by Alex. Agassiz [1878, p. 75] in support of Walcott's claim that the trilobites swam on their backs, as follows:
"An additional point to be brought forward to show that the trilobites probably pass the greater part of their life on their back, and died in that attitude, is that the young Limulus generally feed while turned on their back; moving at an angle with the bottom, the hind extremity raised, they throw out their feet beyond the anterior edge of the carapace, browsing, as it were, upon what they find in their road, and washing away what they do not want by means of a powerful current produced by their abdominal appendages."
Patten [Origin of Vertebrates from Arachnids, p. 363] in the endeavor to correlate the neural (dorsal) surface of Pterichthys or of the fishes in general with the neural (ventral) surface of the merostomes assumes that the position of the eyes depends largely on the position of the animal in swimming, adding: "In Pterygotus, for example, where locomotion was probably largely effected by swimming on the haemal (dorsal) surface, the eyes have already become lateral—a position very unusual in Arachnids. This change is readily explained, since the original position in the embryo of all arthropods is neural; moreover, the history of arthropod eyes shows conclusively that they can assume any position the method of locomotion may demand." In citing further evidence for his claim of important resemblances between the cephalothorax of arachnids and the head of vertebrates, the same author says [p. 365]: "The trilobites probably swam, if at all, on their backs; and it is still more probable that the Merostomata, from their shape and the position of their oarlike appendages, swam in the same way. The larvae of Limulus, according to my own observations, always swim on their backs. Thus the way is prepared for the manner of locomotion in fishes." In view of the great contrast in the shape of their bodies, we doubt the propriety of comparing the swimming mode of the young Limulus with that of such eurypterids
