124 w - J- CROZIER. 



of rays, i.e., depending on the total water requirements of the 

 locomotor organs; or (2) the multiplicity of madrepores is 

 adaptively related merely to the habit of self-division. At first I 

 was inclined to entertain the former idea ; the fact, however, that 

 7-, 8-, and p-rayed individuals, as well as those of 5, 6, or 7 rays 

 and of large size, do get along quite well with a single madre- 

 pore is more favorable to the second notion. 



I would regard it as possible, then, that the multiplication of 

 madrepores at separated points on the disc of Coscinasterias 

 furnishes merely an assurance that portions of the body separated 

 by autotomy will each be provided with a madreporic canal. It 

 is not improbable, however, that the very development of super- 

 numerary stone-canals, by furnishing each an additional " physio- 

 logical anterior point," such as that revealed by Cole's ('13) 

 experiments with Asterias, provides automatically the very 

 conditions determining self-division. 



III. 



The probability of this explanation of the significance of the 

 madrepore might be tested by determining the direction of pro- 

 gression in various individuals, under non-directive stimulation. 

 I studied from this standpoint the locomotion of 12 Coscinas- 

 terias. Non-directive conditions were secured very much as in 

 Cole's ('13) experiments: an 8-c.p. filament, the only source of 

 light, was suspended in the axis of a circular aquarium tub 3 feet 

 in diameter, and 4 feet above the surface upon which the starfish 

 crept. The tub held sea water to a depth of 10 cms. One half 

 hour elapsed between trials. The observations were made at 

 night. To horizontal light of this intensity, Coscinasterias was 

 slightly photonegative, but more intense illumination was required 

 to cause decided negative movements. Even under the supposi- 

 tion that illumination of a larger ray might lead to the determina- 

 tion of directed photonegative movements when the animal is 

 illuminated vertically, owing to the larger sensory surface of such 

 a ray, the conditions here established must be regarded as essen- 

 tially non-directive, because the starfishes often crawled with 

 some other than the longest ray in advance. 



The length of the rays and the number of madrepores pre- 



