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LEON J. COLE 



which Preyer worked (which seems permissible considering the 

 essential similarity of the records) the 'physiological anterior/ 

 as determined by the direction of locomotion, is the interradius 

 ea. 



Finally, if we combine Preyer's results with those obtained 

 on Asterias forbesi, making a total of 683 trials with five differ- 

 ent species of starfish, the result is as follows: 



Here it will be seen that the plane of bilaterality passes through 

 e, which is by this token the 'physiological anterior.' 



2. Echinoids and other echinoderms 



Aside from the few experiments of Preyer on ophiurans, and 

 which he mentions only in a general way as giving negative 

 results (see p. 25), no effort appears to have been made to 

 determine definitely whether preference is given to a particular 

 ray or radius in the other groups of echinoderms outside the 

 asteroids. Grave has already been quoted (p. 23) as saying 

 that in Ophiura 'each arm is equally capable' of acting as direc- 

 tor, and this appears to be the general impression. 



What has just been said of the ophiurans may apparently be 

 applied equally well to the radial sea-urchins — that is, that 

 they may crawl with any part of their circumference in advance. 

 There are, however, certain echinoids which have assumed a 

 secondary bilateral symmetry, and are accordingly especially 

 adapted to locomotion in one particular direction. These are 

 the spatangoids, in some of which the spines all point back- 

 wards, imparting to the creatures somewhat the appearance of 

 a hedgehog. The anus, furthermore, is commonly shifted back- 



