4O C. M. CHILD AND E. V. M. Mi KI1 . 



circles or ovals and the fiber tracts are filled in with dot-. except 

 where a distinct commissure or nerve is concerned; there the 

 direction of the fibers is indicated. Non-nervous structures are 

 not shown except in the case of the alimentary tract, which is 

 diagrammatically indicated where it is present in the sections 

 figured. 



I. THE EXPERIMENTAL PRODUCTION OF TERATOPHTHAI.MK .\\n 



TERAIOMORPFTC FORMS. 



The senior author has given the names " teratophthalmic ' 

 and "teratomorphic" to certain types of head which appear 

 under certain conditions in the regulation of pieces of Plannr'ui. 

 The teratophthalmic head (Child, 'ua, pp. 278-9; 'lie) is one 

 in which the eyes show some departure from the usual structure 

 or arrangement, but the head is otherwise normal in form. The 

 teratophthalmic forms may be divided into several groups ac- 

 cording to the character of the eyes, for these may be "abnormal " 

 in position, size or number or the pigment cups may show tlir 

 most various degrees of fusion (e. .(,'., Fig. 6 below). 



The teratomorphic heads (Child, 'nr) represent a more ex- 

 treme departure from the norm. In these the abnormalities 

 involve not only the eyes but the shape of the head and the 

 position o! the auricles. The teratomorphic head usually pos- 

 sesses a single median eye and the auricular sense organs appear 

 on the front of the head, either separate (Figs. 10 and 16) or 

 more or less completely fused (Figs. 19 and 2^1. In the senior 

 author's earlier work on Plauaria the teratomorphic hca<l> \\ere 

 not separated from the teratophthalmic (Child, 'i \a), but as the 

 degree of experimental control in the production ot these lorms 

 increased it became desirable to set these peculiar forms apart 

 as a distinct group and to give them a name. 



It is possible, as the senior author has shown in various papers 

 (Child, 'l la, 'l ic, 'lid), to control experimentally by a number 

 of different methods the production of these torms. In general 

 they are the result of conditions which decrease the rale ot the 

 dynamic processes below a certain level determined by existing 

 conditions which is necessary for the- production of normal ani- 

 mals. With the proper experimental conditions they can 1 >r 



