ORIGIN OF MONSTERS 521 



C. THE MORPHOGENETIC FACTORS UNDERLYING THE ORIGIN 

 OF EYE TERATA 



1. Stockard^s inhibition theory 



The analysis of the morphogenesis of ophthalmic terata has 

 been attempted repeatedly and with varying success. Good 

 reviews of the opinions of the earher writers on the subject were 

 already given by Spemann ('04), v. Hippel ('09) and Schwalbe 

 and Josephy('13), and to these the reader maybe referred. No 

 distinction is made by most authors between the various degrees 

 of the synophthalmic condition and cyclopia, i.e. the presence 

 of a single median eye. Thus, their interpretation of the morpho- 

 genesis of cyclopia, apphes to the whole so-called 'cyclencephalic' 

 group. 



Two views have been advanced to account for the morpho- 

 genesis of these monstrosities. According to the one represented 

 by Huschke ('32), Dareste ('91) and very recently advocated 

 by Stockard ('09, '10 a, '13) 'cyclopia' is a condition in which 

 the separation of what they consider the originally single optic 

 anlage has been inhibited. 



Opposed to this view is the theory of fusion of two optic 

 vesicles as underlying the formation of 'cyclopia,' which was 

 originally advanced by Meckel ('26), and which in a modified 

 form has recently been advocated by most investigators of the 

 subject and particularly by Spemann. 



This author (Spemann '03, '04) has with an entirely different 

 object in view constricted eggs of Triton taeniatus by placing 

 in the two-cell stage a ligature around the first cleavage furrow 

 in relation to which it was somewhat oblique. As a result of 

 this operation he obtained embryos in which the anterior end 

 was doubled to a greater or less degree, depending upon the 

 degree of constriction. In many of the embryos thus treated 

 Spemann observed that one of the doubled heads (or parts of 

 the head) thus resulting was normal while the other which, 

 owing to the obhque hgature was narrower, had defective, usually 

 synophthalmic and sometimes cyclopean eyes. Since the eye 

 deformity was mostly found on the part distal from the embryo's 



