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THE AMERICAN NATURALIST [Vol. XLIX 



Of these, 4 had 5 long rays, 4 had 6, 2 had 7, 1 had 3 and 

 1 had 4 (see Fig. 11). The addition of new rays during 

 adult life is, so far as known, unusual among starfish, ex- 

 cepting in the multiradiate forms (cf. Bitter and Crocker, 

 1900; Clark, 1907; M'Intosh, 1907). The twelve cases 

 found in A. tenuispina may mean merely that a single ray 

 has been cast off and is being regenerated, for there is 

 found about the same percentage of naturally occurring 

 regenerating examples of A. vulgaris (King, 1898; 1900). 

 Yet I am inclined to interpret this condition as indicating 

 the way in which the modal hepta-radiate form is derived 

 from the fundamental penta-radiate one, or from a hexa- 

 radiate plan, if the young of A. tenuispina be like the post- 

 larvae of Pycnopodia (Bitter and Crocker, 1900) previous 

 to self-division. 3 The three smallest Asterias seen had 

 6 rays. These were subequal and 8 ± mm. long. Other 

 specimens, slightly larger, had either 7 or 8 rays. 



Cases such as those illustrated in Fig. 13 may further 

 prove that addition of new rays occurs independently of 

 the reformation of rays subsequent to self-division. 



VI. The number of madreporites in A. tenuispina is 

 also variable, as noted by Ludwig (1897, p. 358) and 

 others. The number of madreporic bodies is certainly not 

 correlated with the size of the starfish. One of the small- 

 est ones seen had 8 rays* and 5 madreporites, its mean ray 

 length being 10 mm.; while the largest animal collected 

 had 5 rays, with a mean ray length of 70 mm., and but one 

 madreporite. The table in Fig. 14, which includes all 

 cases in which the madreporites were counted, shows that, 

 while the distribution of these bodies is irregular, their 

 number is to some extent correlated with the number of 

 rays. Ludwig gave it as his opinion that there was no 

 correlation of this sort. The relation stands out more 

 clearly if only those individuals having equal rays (and 

 therefore presumably "full grown") are included (Fig. 

 15). Unfortunately, the number of animals is small. 



Multiple madreporites were noted in 5 out of 101 ex- 



3 According to Clark's (1907) studies, the young Heliaster has five rays 

 only; his results throw considerable doubt upon the correctness of the 

 conclusions of Hitter and Crocker. 



