336 On the Variations of certain Crustacea. 



races are so far separate, tliat intermediate individuals, par- 

 taking 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 to the youngest 

 stages of growth. . . . Many species may, no doubt, 

 have been founded on characters no more distinct than these, 

 and on mere deviation of character in the joints, which a 

 critical investigation would prove to be worthless." 



When the advocate of immutability urges the absence of 

 forms intermediate between distinct species, he forgets that 

 between acknowledged varieties it is mostly impossible to obtain 

 connecting links. 



Besides forms, varieties, and nearly allied species observed 

 in places near to each other, Dr. Claus notes examples of 

 variation depending on influences of climate and other external 

 conditions. He lays little stress on varieties of colouring, but 

 much upon difference of size, instancing the Cetochilus sep- 

 tentrionalis as found at Nice, which is only one-third of the 

 normal size of the species. The little Galanus mastigophorus 

 which he distinguished at Messina by the long-, whip-shaped, 

 antennal setae, occurred also at Nice, but without these seta?. 

 Very remarkable also are the differences of form in the male 

 prehensile foot of Dias longiremis. While the fifth feet of 

 the females of Nice and Heligoland are in all essential respects 

 the same, that of the Nicasan male has a stronger claw and 

 appendage, to allow, as it seems, of a stronger grasp. We 

 have here, as in the case of Orchestia Darwinhi, two different 

 males in the same species, and can only explain the deviation 

 as the result of natural causes connected with different localities. 

 The difference of the feet is indeed so striking as to have led 

 to the supposition of the two forms being distinct species. An 

 instance of concurrent variation of different parts of the body 

 occurs in the IcMhyoplwrba denticomis of Nice and Heligoland. 

 The former is not only smaller than the northern species, but 

 has proportionally far more slender armatures of the antennae, 

 and a much less marked angular projection of the last segment 

 of the body, and in the males much weaker prehensile appa- 

 ratus of the fifth foot. It thus stands, in size and conform- 

 ation, between the northern I. angustata and denUcornis, the 

 distinctions, indeed, are here so sharply defined that according 

 to some schools of naturalists they might properly constitute 

 species rather than varieties. " The opponent of the origin of 

 species by descent," continues Dr. Claus, "asks to sec fori 

 an intermediate character. When we succeed in showing 



