STRUCTURE AND DEVELOPMENTAL RATE 211 



anterior or posterior regions. Nevertheless, from what we have 

 seen of the tendency on the part of the smaller component in 

 the completely double individuals to possess poorly developed 

 head ends, it would not be surprising to find that ophthalmic 

 tissue and other cephalic structures were frequently absent from 

 pelvic teratomata, though such structures might in certain cases 

 be particularly evident. 



5. Types of defects exhibited by the smaller component. We may 

 now return to a brief consideration of the types of deformities 

 shown by the smaller components in the unequal pairs and 

 decide whether these defects are similar in kind to those which 

 occur in nature, as well as those experimentally induced, among 

 single individuals. 



In the first place, it is noted at once that ophthalmic deformities 

 are particularly frequent. The illustrations show complete 

 anophthalmia, monophthalmia, and typical cyclopean conditions 

 as well as various degrees of imperfection in the individual eye, 

 such as coloboma and reduction in size of the retinal region. 

 Duplicities produced by any method such as the mechanical 

 constriction employed by Spemann, as well as those occurring 

 in nature, show in the smaller component the same ophthalmic 

 defects as are found among these double specimens induced by 

 development in low temperatures or with insufficient oxygen 

 supply. 



The brain in the smaller "components shows various abnormal 

 contours or may be simply tubular in shape without a normal 

 expression of bilateral diverticula or hemispheres. 



The mouth is often deformed and frequently absent and the 

 operculum and branchial arches are distorted in shape. The 

 fins are often small and underdeveloped. The general body 

 shape may be variously modified, the caudal end being short 

 and stumpy or absent. The heart may be poorly developed 

 and pulsating feebly so that the blood fails to circulate and 

 becomes massed in various regions of the body. 



It is unnecessary to do more than enumerate these defects 

 and examine the illustrations to convince anyone familiar with 

 the commonest developmental anomalies that the structural 



