2 LEON J. COLE 



plate. The ray e is used 89 times out of the 95, and the next greatest 

 numbers are shown by the two rays lying on either side of e, namely 

 a (56) and d (43). The combination of the two rays lying at the sides 

 of the madreporic plate (a + e), was used 37 times. On the other 

 hand, the rays lying opposite (6 and c) were used but rarely, and not 

 once in the whole 95 experiments ivas the pair b -\- c used in combination. 



To make this statement intelligible, it will be necessary to 

 explain the notation used by Jennings in designating the various 

 rays. This is shown in figure 1, which is reproduced from the 

 diagram given by Jennings. Beginning with the arm at the 



Fig. 1 Diagram of starfish, showing notation of rays with respect to position 

 of madreporic plate (from Jennings '07). Preyer designated arms a, h, c, etc., as 

 1, 2, 3, etc. respectively (cf. p. 24). For comparison with the system adopted 

 by Loven, and in common use by specialists, see figure 9, p. 28. 



right of the madreporite (the right hand member of the 'bivium') 

 and going clockwise, the arms were designated arbitrarily by 

 the letters a to e respectively. Thus it will be seen that 6, c, d, 

 compose the 'trivium', while e is the left hand member of the 

 'bivium.' 



The question at once suggests itself: What is the reason 

 that the rays of a certain region are used most often in the right- 

 ing process? Does it mean possibly that there is something 

 akin to an antero-posterior^ differentiation? It would be inter- 



2 It must be borne in mind that 'anterior' and 'posterior' are here used in rela- 

 tion to the assumed position of the starfish in its natural locomotion, and not 

 in their morphological sense. 



