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THE AMERICAN NATURALIST [Vol. XLIX 



variety of conditions, especially the rapid growth of re- 

 generated rays. The regenerating rays of Linckia (Clark, 

 1913; Monks, 1904) and the newly formed rays of multi- 

 radiate types (Ritter and Crocker, 1900) grow more rap- 

 idly than the old ones and soon reach the dimensions of 

 the latter; this is also indicated in my series. But the cor- 

 relation of the number of long with the number of short 

 rays (using only those cases in which the two groups were 

 clearly distinct) makes it evident (Fig. 11) that the condi- 

 tion in which there are 3 or 4 long rays and 4 short ones is 

 by far the most common; and further, that the cases in 

 which there are either 3 or 4 long rays are almost equally 

 abundant. It seems not unlikely, then, that A. tenuispina 

 usually has 7 rays before it divides, and that it divides 

 into two parts having, respectively, 3 and 4 rays, the divi- 

 sion-surface then giving rise, in the greater number of 

 cases, to 4 new rays, but sometimes to 5, 3 or even 2. 



If all the individuals observed had undergone autotomy 

 and regeneration according to this scheme, then those 

 with 7 and those with 8 rays would be expected to occur 

 in equal abundance ; 8 is next in frequency to 7, but the 

 latter preponderates because some starfishes have prob- 

 ably not autotomized at all, and because all the animals 

 which have divided do not adhere to this paradigm (see 

 Fig. 11). Yet, in the majority of cases, 4 rays are regen- 

 erated whether there are 2, 3 or 4 long (old) rays in 

 evidence. 



It would seem that self-division may occur at any time 

 in the life history of A. tenuispina, or at least in animals 

 of all sizes, though it is my impression, gained from hand- 

 ling many live individuals, that the smaller (younger ?) 

 ones autotomize more readily than larger ones. Those 

 showing two distinct ray groups ranged in longer ray 

 length from 11 mm. to 65 mm. There is no evidence that 

 autotomous divisions follow one another rapidly, or in- 

 deed that they occur more than once in any given indi- 

 vidual. 



One case was observed in which there was one long ray 

 only, and 6 shorter ones. This may mean that a single 

 ray can regenerate the whole body, as suggested by v. 



