SUSCEPTIBILITY OF AMPHIBIAN OVA TO X-RAYS 443 



rule, are differentiated. In some specimens nasal fossae may be 

 traced from the exterior to the pharynx by a column of cells con- 

 taining an imperfect lumen or the column of cells may not reach 

 the pharynx. Development on one side of the body may be much 

 more advanced or less abnormal than that on the other side. 



Ear. Larvae with fairly distinct heads are rarely found in 

 which the auditory vesicles are not formed. In most cases the 

 early stages of development in the vesicle seem fairly normal, 

 but after the vesicle has been cut off from the ectoderm and the 

 dorsal diverticulum has been given off differentiation, as a rule, 

 ceases, unless the larva is relatively little affected. Extreme types 

 of abnormality in the vesicles have not been found in the speci- 

 mens studied. 



Alimentary canal and its appendages. During the earlier 

 stages of larval differentiation the archenteron may become 

 abnormally dilated or it may be abnormally contracted. As the 

 alimentar}^ canal differentiates the abnormalities may become 

 especially marked at the anterior or posterior end or may be 

 quite general in character. In most of those larvae which become 

 fairly well differentiated there is formed a mouth with an opening 

 into the pharynx. The lips and jaws are usually rudimentary 

 but the abnormalities which affect them are quite varied. 



In one instance the epithelium was entirely missing on one 

 side of the pharynx. Patent gill slits may be formed but external 

 gills are rarely well formed and internal gills are differentiated 

 only in those forms which are comparatively slightly affected. 

 A well marked operculum is seldom formed. The oesophagus 

 becomes patent in some specimens but remains closed in others. 

 The stomach in the most advanced specimens curves to the right 

 but is, as a rule, rudimentary. The intestines generally show only 

 a slight coiling and may be represented by a single straight tube. 



Vascular system. In nearly all of the specimens showing 

 marked abnormalities in body form during the latter part of 

 larval differentiation the vascular system is profoundly affected. 

 In the more extreme forms it is represented by abnormal rudi- 

 ments of the heart and larger vessels. In some instances not 

 even these may be distinguished. The heart, as a rule, is differ- 



