290 MORGAN. [VOL. I. 



10, ii, and Fig. 7). In the male the anterior abdominal append- 

 ages are smaller (Figs, 4, 5), and only the second, third, 

 fifth, and sixth appendages are present. The abdominal append- 

 ages of the female (second, third, and fourth) carry the eggs 

 during the breeding season. These appendages are supplied 

 with long hairs, to which the eggs are attached. In the male 

 the hairs are not so well developed. 



The last abdominal appendages (Fig. 7) are hard and strong 



- the left one much larger than the right. These appendages 



seem to play an important part in anchoring the abdomen in 



the shell. So securely is the abdomen fastened that it will often 



pull apart before the appendages loosen their hold. 



Are any of these appendages rudimentary ? A statement 

 that this or that part is rudimentary implies a knowledge of the 

 descent of the animal possessing such structures. A simple 

 reduction in size, moreover, is not a criterion, because a smaller 

 appendage may be in certain cases a more perfect adaptation 

 than a larger one. For instance, most zoologists would admit, 

 I think, that the fourth and fifth pairs of thoracic legs of the 

 hermit crab have been reduced in size, but how far this reduc- 

 tion is due to degeneration and how far to new adaptation is 

 difficult or impossible to say. In comparison with most other 

 Decapoda these appendages seem reduced, and they have lost 

 their locomotor function. 



In the abdominal region the evidence in favor of a reduction 

 or rudimentary condition of the appendages of the male is 

 stronger. On one side the appendages have entirely gone, and 

 on the other side they are small and weak, and the third appendage 

 (on the fourth segment) has completely disappeared. In other 

 related forms the two anterior abdominal appendages of the 

 male have also entirely gone, or are represented by only a few 

 tufts of hairs. 



The terminal appendages, on each side of the telson, do not 

 appear reduced in comparison with the similar appendages of 

 other Crustacea, but one is nearly twice the size of the other 



(Fig- 7)- 



