BILATERAL TENDENCIES IN PYCNOPODIA HELIENTHOIDES. 25! 



ever, the modal point in both the male and female is seen to be 18. 

 The adult cannot be determined by the number of rays, because 

 the immature star may reach the modal point in number of rays, 

 and like mature specimens go beyond the modal point, and even 

 not reach maturity, while on the other hand mature male speci- 

 mens may be found to have only 13 rays, which is reaching down 

 into the immaturity limit. Mature specimens spoken of here 

 have special reference to sexual maturity for that season. The 

 modal point of both males and females is practically the same. 

 This is demonstrated by a number of specimens examined in 

 the same region on the same day, and represented by Fig. 4, 

 /, A (male), //, B (female). As a matter of fact, the average 

 number of rays in the male, female and immature is almost the 

 same, which goes to show that radial development occurs in the 

 comparatively early part of the life of the individual star. On 

 this occasion, the depth for and the diameter of every specimen 

 was measured; and the number of rays present, and the sex 

 was determined. These findings were as follows: 



1. The average depth at low-tide for 75 specimens found in a 

 belt 30 feet wide by \ of a mile long was 4.76 feet. 



2. The diameter measured along the median axis from tip to 

 tip of odd anterior and odd posterior rays for immature was 8.21 

 inches, and the average number of rays was 17.85. 



3. The average diameter of the males was 13.5 inches, and the 

 average number of rays was 18.56. 



4. The average diameter of the female was 13.6 inches; the 

 average number of rays was 18.8. 



SUMMARY. 



1. Pycnopodia is highly bilateral when moving about in its 

 natural abode. It uses the same side always as anterior end. 



2. During righting reactions, this same side almost always 

 takes the initiative and the greatest number of rightings are 

 made in that direction. Repeated rightings do not improve 

 its speed. 



3. It is hardly ever found on dry land; its movements are 

 swift enough so that it keeps below the tidal mark; it moves 

 swiftest when stimulated from within. 



