1 8 UNIVERSITY OF MISSOURI STUDIES [_2o6 



In my experiments upon these appendages in the crayfish 

 I have not been very successful. In several cases individuals ex- 

 perimented upon did not live long enough to show any signs of 

 regeneration. However, among specimens brought into the lab- 

 oratory I have found several regenerating these appendages. 

 On November 21, 1898, I obtained an individual which had lost 

 the entire left, sixth abdominal appendage, but at the time I 

 found the crayfish, regeneration seemed to have advanced as far 

 as would be expected before a moult. The moult took place on the 

 twenty-first of the following April, and at that time the appen- 

 dage expanded to three-fourths the size of its fellow of the right 

 side, and in every respect was perfectly normal, its articulations 

 and setae being complete. Compare Figs. 14 and 15, PI. I. Fig. 

 14 shows the tail-fin with regenerated left appendage before the 

 moult had taken place, and Fig. 15 the same after the moult. 



Several other similar instances have come under my notice 

 during the course of my observations. I recently found in a 

 collection of C. gracilis a small crayfish, about 20 mm. in length, 

 that had lost almost the entire telson, yet a new and apparently 

 perfectly normal one was being regenerated (Figs. i6-i7, PI. 

 I). Fig. 16 shows a dorsal view of this regenerating telson en- 

 larged ten times. Evidently no moult had taken place since the 

 injury, for the articulation between proximal and distal seg- 

 ments is only partially outlined, and only a few irregular, short 

 setae are present. The new telson is not perfectly symmetrical. 

 A ventral view is shown in Fig. i7. The indications are that the 

 entire telson had been removed, yet the regenerated anal orifice 

 is perfectly normal, except that it is somewhat nearer the poste- 

 rior end than in an uninjured telson. 



3. SWIMMERETS. 



My experiments upon the swimmerets have not been very 

 extended, but I have found none to regenerate except the first 

 pair in the male, which are modified as accessory reproductive 



