128 W. J. CROZIER. 



greatly differing in size, the directive ray appears to be one next 

 to the plane of antecedent autotomy. This fact might seem un- 

 favorable to the conception of the "cause" of autotomy above 

 formulated, but in fact I found that if the creeping of halves of 

 starfishes recently separated was studied, the results were, on the 

 contrary, favorable to this conception. Examples in point are 

 afforded by such specimens as are illustrated in Fig. 6. 



IV. 



Summary. It has been pointed out that in those individuals 

 of Coscinasterias tenuispina which divided autotomously more 

 than one madrepore is developed on the disc previous to division. 

 Further, that each madrepore, or group of madrepores, is an ex- 

 ternal sign (at least) of the development of a tendency toward 

 the establishment of a "physiological anterior" point, as ex- 

 pressed in creeping. Hence it is suggested that the cause of the 

 autotomous separation of the body of this starfish into two ap- 

 proximately equal parts each as a rule then automatically re- 

 ceiving one or more madrepores may be intimately connected 

 with the very development of these structures. It is shown that 

 this asexual multiplication by self-division exhibits a seasonal 

 rhythm so adjusted as to constitute a propagative method which 

 supplements, in point of time as well as in kind, the ordinary 

 gametic reproduction, the former method being distinctly in abey- 

 ance during the winter months (Januarys-February), when breed- 

 ing occurs. 



CITATIONS. 

 Agersborg, H. P. K. 



'18 Bilateral Tendencies and Habits in the Twenty-rayed Starfish, Pycno- 



podia helianthoides (Stimpson). BIOL. BULL., Vol. 35, pp. 232-254. 

 Clark, H. L. 



'i3a Autotomy in Linckia. Zool. Anz., Bd. 42, pp. 156-159. 

 'i3b Investigations on Echinoderms at Montego Bay. Year Book n, Car- 

 negie Instn., Wash., pp. 134, 135. 

 '15 Commatulids of Torres Strait: with Special Reference to their Habits 



and Reactions. Publ. Carnegie Instn. Wash., No. 212, pp. 97-125. 

 Cole, L. J. 



'13 Direction of Locomotion of the Starfish (Asterias forbesi). Jour. Exp. 



Zool., Vol. 14, pp. 1-32. 

 Crozier, W. J. 



'15 On the Number of Rays in Asterias tenuispina Lamk. at Bermuda. 

 Amer. Nat., Vol. 49, pp. 28-36. 



