Geology and Mineralogy. 459 



Concerning the early stages of growth and the larva? of scor- 

 pions, they sum up as follows : 



" We consider as coenogenetic or purely larval the relatively 

 larger size of the carapace, of the compound eyes and of the 

 swimming legs, and the smaller number of the abdominal seg- 

 ments ; as palingenetic and phylogenetic, the approximation of 

 the compound eyes to the margin, the prominence of the ocelli 

 and their tumescences, the lack of differentiation of the abdomen 

 and the smaller size of the telson. In these palingenetic charac- 

 ters the nepionic stage resembles so much the Cambric Strabops, 

 that we shall designate this as the Strabops stage " (122-3). 



"We may say that, (1) the general homologies of the two 

 [embryonic and larval stages of the scorpion and the larvae of the 

 eurypterids] are very apparent in the composition of the carapace 

 and abdomen of an equal number of segments, but that, (2) while 

 in the scorpion the segmentation is completed long before the 

 hatching, in the eurypterids the larvae in the nepionic stage still 

 lack the full complement of segments, recalling the trilobites in 

 this feature and clearly representing a more primitive condition ; 

 (3) there are a number of distinct differences in the larvae of the 

 eurypterids and of the scorpions, some of which lie in the form of 

 the carapace, the early embryonic differentation of the pedipalps 

 from the other appendages, the strong prelarval differentiation of 

 preabdomen and postabdomen and the disappearance of the 

 abdominal appendages in the scorpions and their persistence in 

 the eurypterids" (145-6). 



" The early appearance and later atrophy of the abdominal 

 appendages is clearly a feature that points to a common ancestor 

 for the scorpion and the eurypterids having such appendages, and 

 we believe that the cephalothorax in the embryo of the scorpion 

 retains ancestral features from the facts that its length corresponds 

 to about six abdominal segments and it equals the latter in width ; 

 that, however, the strong development of the procephalic region 

 is tachygenetic. 



" A comparison of the larvae of all three, the eurypterids, 

 Limulus and the scorpion, shows both the latter to have lost the 

 primitive form of the abdomen by acceleration, that of Limulus 

 being much broadened, that of the scorpion abruptly contracted 

 to the tail or postabdomen while the eurypterids have best pre- 

 served the original gradual and uniform contraction. The cara- 

 paces of the eurypterids and the scorpion have most nearly 

 retained the original proportions and form of the common ances- 

 tor. Of the cephalothoracic appendages the chelicerae are alike 

 in all three groups and obviously ancestral in their form ; the 

 remaining legs have taken quite different courses of adaptation, 

 the scorpions having developed the powerful chelate pedipalps, 

 the eurypterids the swimming legs, while those of Limulus 

 have remained relatively undifferentiated, and show no tachy- 

 genetic features in the embryos except the chelae. The embryo 

 of the scorpion shows simple walking legs, like those of the 



