DACTYLOPUS. 109 



ing in mobility ; the antennas clumsy, with their third 

 and fourth joints short and thick, the second joint 

 very long ; the second foot-jaw ends in a strong, mas- 

 sive, clasping hand ; the first pair of feet are armed 

 with doubly-curved claws ; the feet, especially the last 

 pair, are strong and clumsy, all the setas showing a 

 tendency to become plumose. The smaller and slen- 

 derer breed has larger antennas, the third and fourth 

 joints of which are much elongated ; the prehensile 

 apparatus of the foot-jaws and first pair of feet more 

 slender, and there is also a much slimmer, slen- 

 derer form of the limbs. In general structure and 

 conformation of body, in the peculiar arrangement 

 of setaa, the serration of the abdominal segments, in 

 short, in those points where distinct species mostly 

 diverge, there is here a striking agreement. 

 After diligent inquiry, these differences remained un- 

 explained, and I was inclined to consider them as 

 mere individual variations. But further investigation 

 of all parts of the body convinced me that two distinct 

 forms, with qualities diversely useful, had originated 

 two separate races, one slender, swift, and agile, the 

 other clumsy in figure, but robust and powerfully 

 armed. The two races are so far separate that inter- 

 mediate individuals partaking of the characters of both 

 are not met with. The upper antennas, however, in 

 each case show a tendency to similar variations ; at 

 the same time these variations are not so profound 

 that they might not have been acquired singly or in 

 combination. The differences in the relative size of 

 the claws and prehensile organs may be traced back 



