350 Charles Zeleny. 



The crayfish were kept in individual wide-mouthed bottles, 

 which were inclined at a slight angle to the horizontal and were 

 covered with pieces of cheese cloth held in place by rubber bands 

 (see Fig. i). The crayfish were fed every fifth day on frog meat 

 or beef, the water being changed immediately after the meal. 

 Under these conditions no difficulty was experienced in keeping 

 the animals alive. The tew deaths recorded during the course of 

 the experiment were for the most part due to neglect in changing 

 the water immediately after the meal. Such a suspension of 

 ordinary care is especially liable to be fatal when occurring soon 

 after a moult. The operation on the majority of the crayfish was 

 performed October 12, 1904, and the experiment was closed April 

 20 after an interval of 181 days. A small minority comprising 16 

 individuals was operated on two days later and kept until April 22, 

 the interval being likewise 181 days. 



3. DATA. 



The records of the experiment include the sex of the animals, 

 the date of moulting, and the length in millimeters of the thorax 

 and of the chelre after each moult. The size of the regenerating 

 walking legs of each individual in Series B is approximately 

 expressed in my notes in fraction of the legs which are being 

 replaced. The latter data are, however, not given in the tables 

 reproduced in the present paper. In these tables (pp. 352 to 358) 

 the moulting time is given in days after the operation. The 

 thoracic length is the distance in millimeters between the posterior 

 edge of the thorax and the base of the thoracic spine. The chela 

 length is the greatest length in millimeters of the next to the last 

 segment of the chela, the propodite. 



The data are given in Tables I, II, III and IV. The males and 

 females are separated because the rate of moulting and of regener- 

 ation was found to be different in the two sexes. The individuals 

 in each table are arranged in order of thoracic length after the 

 first moult. In the columns giving the original lengths, i. e., the 

 lengths before the operation, blank spaces indicate that the meas- 

 urements were not taken. In the other columns a blank space 

 indicates that the animal had not moulted when the experiment 

 w^as closed, 181 days after the operation. In the last column the 



