REMOVAL OF NASAL PITS AMBLYSTOMA EMBRYOS 29 



connections. The problem lies in making a lesion that will cause 

 Gudden's atrophy, and then in keeping the animal alive suffi- 

 ciently long for the atrophy to reach its height. 



In the spring of 1911, Dr. R. G. Harrison suggested that the 

 removal of the nasal placode of Amphibia would be a practical 

 method to attack such problems. Frog larvae were first used 

 for the experiments but as Bell showed in 1907 the placodes often 

 regenerated, a fact which would destroy the value of the material 

 for this study. Bell found this regeneration occurred in a large 

 number of cases, even where it was believed the placode had been 

 entirely removed. This regeneration may have been due to the 

 fact that the regenerating area about the placode was not 

 removed. 



In Amblystoma, the placode can be easily extirpated. The 

 nasal Anlage is readily distinguished from the surrounding tissue, 

 and hence complete removal is a relatively simple matter. 



In the course of the experiments it was found that the extir- 

 pation of the nasal placode made possible not only a study of 

 the neurological problems involved, but also a part, at least, of 

 the developmental mechanics of the skull. Since the material 

 for this morphological work was kept alive for some months, a 

 study of the reactions to food stimuli of the operated and normal 

 forms was also undertaken. These three aspects of the problem 

 form the body of the following report. Owing to the difficulty 

 encountered in keeping operated forms alive through metamor- 

 phosis, the report of the histological changes in the telencephalon 

 as a result of the operations must be deferred until later. 



MATERIAL AND IVIETHODS 



Amblystoma larvae 5-6 mm. long, were used for all of the oper- 

 ations, of which two series were performed. In the first the nasal 

 placode of the right side only was removed; in the second both 

 were extirpated. The material obtained from the first series 

 served as a basis for the morphological investigation — that from 

 the second for the physiological experiments and as a check for 

 the morphological study. 



