REMOVAL OF NASAL PITS AMBLYSTOMA EMBRYOS 31 



of a regenerating capsule. Later study by means of sections 

 added two more to the number. 



A number of experiments were then performed on the frog, em- 

 bryo to see if there was any difference in the behavior of the nasal 

 anlage in two such closely allied forms. Great care was taken to 

 remove all of the nasal placode. It was apparent from the out- 

 set that the placode of the frog is not nearly as compact nor so 

 clearly differentiated from the surrounding ectoderm and not so 

 easily separated from the underlying mesenchyme as it is in 

 Amblj^stoma. Hence the complete extirpation is a much more 

 difficult and delicate matter. External inspection showed twenty- 

 two regenerating capsules out of seventy-six operations. Sections 

 of a number of the remaining fifty-four taken at random showed 

 an occasional abortive pit. It is evident then, that complete 

 extirpation in the frog does preclude regeneration quite as com- 

 pletely as in Ambly stoma. It is possible that here, as in the 

 regeneration of the limbs, lens and gills, there is a circumscribed 

 area about the anlagen which on the removal of the "anlagen may 

 regenerate it. Apparently in the frog this regenerating area is 

 less restricted than in Amblystoma, if any such is present in the 

 latter, 



REACTIONS OF NORMAL AND OPERATED LARVAE 



Turning now to a consideration of the experimental study of 

 Amblystoma, it is obvious that by removing the nasal placodes 

 of both sides previous to the formation of nerves, it is possible 

 to obtain larvae which have never possessed functional olfactory 

 organs. Thus is afforded excellent material for a comparative 

 study of the reactions of noseless larvae and normal larvae to 

 olfactory stimuli without the introduction of secondary factors 

 due to shock or discomfort as a result of the operations. 



Parker ('10) was the first to show conclusively that aquatic 

 animals react positively to the olfactory stimulus of food. By 

 suspending two bags in an aquarium, the one containing cheese 

 cloth, the other bits of worm, he was able to detect distinct posi- 

 tive reactions of Ameiurus to the bag containing the food mate- 



