223J REGENERATION OF CRAYFISH APPENDAGES 35 



icle. The horn-like appendage is shown from the side together 

 with the antenna (at) and antennule (an) from the same side. 

 The rostrum has been cut away so as to better expose the regen- 

 erated part. A similar type of structure is indicated in Fig. 32 

 at n. Here, however, there are three segments and the rounded 

 base, and the arrangement of the segments gives the appendage 

 the appearance of having been spirally twisted. As in the pre- 

 ceding case, the whole appendage is covered with a dense cut- 

 icle and possesses no movable articulations. The regenerated 

 structure shown in Fig. 34 (m) consists of six segments but 

 lacks the rounded elevated base. In this case, the appendage 

 curves upward and then downward, at the same time twisting 

 inward, towards the median line. In this figure, the antennule 

 is not shown. There is a noticeable difference between these 

 appendages of the crayfish and the somewhat similar structures 

 described by Herbst for the shrimp in the absence of long, sen- 

 sory hairs in the former. It will be remembered that the horn- 

 dhnlichen processes described by Herbst, were thickly beset on 

 the ends and ventral sides by long segmented setae, considered 

 by him to be of a sensory nature. He seems to imply, although 

 he does not definitely state it, that these, in a measure at least, 

 compensate for the loss of the eye. In the case of the horn-like 

 structures in the crayfish, no setae whatever are present and 

 there is no external indication at all that they are more sensitive 

 than a leg or maxilliped. 



Type IV: Unsegmented horn-like structures. The chief 

 difference between this type of regenerated appendage and Type 

 III consists in the fact that here only one segment is regener- 

 ated. Fig. 30, PI. IV, shows a regenerated appendage of this 

 type. The crayfish which furnished this particular instance was 

 a small individual of C. gracilis. On May 9, the entire eye was 

 removed; the individual afterwards moulted on May 18 and 



