io6 Papers from the Marine Biological Laboratory at Tortugas. 



eration, it is necessary to correct the results by obtaining the specific amount 

 of regeneration in each case ; that is, the amount of regeneration divided 

 by the cephalo-thoracic length. When this is done the result shows that 

 the first two successive regenerations at least are equal and there is no 

 change in the power to regenerate as a result of successive injury. 



A comparison of the left chelae in crabs which had been regenerating 

 a right chela with the left chelae in uninjured individuals shows that there is 

 no appreciable change in the left chela as a result of the removal and regen- 

 eration of the right chela. 



METHODS AND DATA. 

 The data are based on observations made upon 197 individuals of the 

 gulf-weed crab during June and July, 1906. Specimens varying in size from 

 3 to 15 mm. were collected and placed in individual dishes, each with a 

 floating piece of gnlf-weed. Each crab was numbered and careful record 

 was made of its molting times and other points of interest. The water was 

 changed every day and the animals were fed on the small fish (atherina) 

 every other day. Care was taken to keep all the conditions as nearly alike 

 as possible in all the dishes. Regular observations were made every morn- 

 ing and at this time cast skins were removed and preserved and necessary 

 operations were made. It was found that the increase in size of the ani- 

 mals was confined to the first day after a molt and all operations were 

 accordingly made a day after the molt, so that the relation to the molting 

 time might be alike in all. The operation in every case consisted of the 

 removal of the right chela as its breaking joint. This was effected by in- 

 juring the nerve of the appendage with a needle or forceps. The removed 

 appendage started to regenerate as a coiled bud inside of a chitinous sac. 

 The first molt succeeding the operation released the new chela from its sac 

 and allowed it to expand to its normal form. The external dimensions 

 remained stationary after the first day following the molt. The regenerated 

 chela was again removed on the day after the molt, and so on, as long as the 

 time permitted. The cast skins of each molt, the removed right chelae, and 

 the final animals were all preserved and measured. A complete record of 

 the history of the animals during the course of the experiments was thus 

 obtained. This gives two series of data. The first gives the normal con- 

 dition of the parts and the second the parts after the first, second, and 

 third regenerations of the right chela. The different stages of each indi- 

 vidual were measured and these and other data are collected in table i. 

 Full explanations are given in connection with the table. The length of the 

 cephalo-thorax is the greatest length (LL) and the width the greatest width 

 {WW) as shown in fig. i. The chela-length is the length of the next to 

 the last segment or propodite, as shown in fig. 2 {LL). It will be noticed 

 in table i that in a great many cases the casts were broken. In most of 

 these the crab had started to eat up its cast before the first day was up. The 

 table includes all the measurements and other data without elimination, since 



