I22 NEW YORK STATE MUSEUM 
The lack of differentiation of the preabdominal and postabdominal 
segments 1s hkewise shown in the embryo and larva of Limulus, while in 
that of the scorpion the two regions are distinguishable almost as soon 
as segmentation sets in, obviously owing to the very pronounced differen- 
tiation between the broad preabdomen and the narrow taillike postab- 
domen in the adult. In the Cambric Strabops there is less differentiation. 
observable between the two abdominal regions than in any later eurypterid 
and the more primitive of these later forms distinguish themselves by a 
more uniform and gradual contraction of the abdomen. It is a wholly 
proper assumption that the undifferentiated condition is the more primi- 
tive. The lack of differentiation of the abdomen in the larvae is hence 
to be interpreted as an inherited palingenetic feature. 
The smaller number of segments in the nepionic stage is, for theo- 
retical and observational reasons, to be considered as a purely larval 
feature incidental to the growth of the organism. The Cambric Strabops 
possesses the same number of segments as the Upper Siluric or Carbonic 
eurypterids and if any change in the number of segments in the develop- 
ment of the higher Arthropoda has taken place, it has generally been a 
reduction. The trilobites with the smaller number of segments in the 
immature stages and the greater number of segments in mature conditions 
of the earlier and more primitive species such as Paradoxides and Harpes, 
furnish an excellent analogy. 
The smaller size of the telson is in accordance with the ontogeny 
of Limulus and is manifestly a palingenetic character indicating the primi- 
tive condition. This view is supported by the short, blunt telson of Strabops 
and the primitive later eurypterids, such as Hughmiulleria. 
In summing up the larval characters observed in these immature 
eurypterids 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 segments; as palingenetic 
and phylogenetic, the approximation of the compound eyes to the margin, 
the prominence of the ocelli and their tumescences, the lack of differ- 
