AN EXPERIMENTAL ANALYSIS OF ASYMMETRY IN 

 THE STARFISH, PATIRIA MINI ATA 



H. H. XEWMAX. 

 (From the Hull Zoological Laboratory, the University of Chicago.) 



I. INTRODUCTION. 



The present paper gives the results of a portion of the experi- 

 mental work carried on at the Hopkins Marine Station of Leland 

 Stanford University in the spring of 1923. The program of work 

 was a continuation and an extension of the experiments begun in 

 the same laboratory in 1920 and published during the next two 

 years (Newman, '21, a; '21,6; '2i,c; '22). 



It became apparent in 1920 that not only twinning but other 

 developmental aberrations could be induced by retarding the rate 

 of development of eggs and embryos in a considerable variety of 

 ways. Of all the agents used by various investigators for re- 

 tarding development, that of low temperatures seemed to be the 

 least open to objection and is perhaps the most readily managed. 

 It was, therefore, with the program in mind, of subjecting Patiria 

 and other echinoderms to various degrees of low temperatures at 

 various stages of development and to observe and analyse the 

 resulting developmental aberrations, that work was begun early 

 in April, 1923. 



During some of the very first of the preliminary experiments it 

 was found that subjection of Patiria blastulee to temperatures of 

 about 2 C. for two or three hours brought about a marked in- 

 crease in the percentage of larvae showing reversed or right-handed 

 asymmetry. For over two months after this discovery it became 

 a major consideration to gather an adequate mass of data on this 

 subject and to work out the implications involved. 



Before it was possible to arrive at any justifiable conclusions as 

 to the affects of low temperatures upon asymmetry it was neces- 

 sary to study in some detail the normal development of Patiria. 

 It seems likely that entirely normal development is unattainable 

 under laboratory conditions, yet the culture methods used were 

 experimentally determined to be a vast improvement upon those 



in 



