author's abstract of this paper issued 

 by the . bibliographic service, june 13 



THE EXPERIMENTAL PRODUCTION OF TWINS AND 

 DOUBLE MONSTERS IN THE LARVAE OF THE 

 STARFISH PATIRIA MINIATA, TOGETHER WITH 

 A DISCUSSION OF THE CAUSES OF TWINNING 

 IN GENERAL 



H. H. NEWMAN 



Hopkins Marine Station of Leland Stanford University and the Hull Zoological 

 Laboratory of the University of Chicago 



FORTY-SIX FIGURES 



THE PROBLEM STATED 



A great deal has been written about twins during the last dec- 

 ade and much interest has been shown in the general biological 

 aspects of twinning, especially in the bearing of twinning on 

 sex determination and sex differentiation, on the limits of hered- 

 itary control, on symmetry reversal, and on the heredity of the 

 twinning tendency. Little attention, however, has been paid to 

 the physiology of twinning: the causal factors responsible for the 

 doubling of normally single individuals or structures. It is the 

 function of the present paper to throw some light upon this 

 obscure problem. 



When the writer first became interested in the biology of twins, 

 the problem of the physiological basis of twinning assumed a 

 different aspect from that which now presents itself. The pro- 

 duction of two individuals or parts, where one would normally 

 appear, was at first thought a supernormal process — a develop- 

 mental excess, due presumably to some extraneous stimulus. 

 It soon became clear, however, that this naive first conjecture 

 was incorrect, for several lines of evidence seemed to point to 

 the diametrically opposite conclusion: that twinning is a sub- 

 normal phenomenon associated with a depressed or retarded 



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