REPRODUCTION OF COSCINASTERIAS. 



127 



stated, the latter factor is, on the whole, preponderant. 5 In 13 

 cases, where the disposition of rays and of madreporites was 

 most favorable, the longest ray was recorded as " director," in the 

 average, for 32.2 per cent, of the trials ; a ray near a madrepore 

 being so recorded, in the average, for 42.2 per cent, of the trials. 



9.0 



FIG. 6. The direction of progression (arrow) in two typical instances of 

 recently autotomized halves of Coscinasterias. a, division surfaces ; non- 

 directive stimulation. 



More convincing than such averages, however, are the actual data 

 already set forth. 



Frequently, in the case of animals having two ray-groups 



5 In connection with the matter of physiological and anatomical polarity in 

 echinoderms, compare Clark's observations on the locomotion of Comatula 

 purpurea ('15, p. 112), and mine on the creeping of Mellita, (Crozier, '20) ; in 

 both forms there is clear evidence of functional bilaterality. 



