j^Iorphological Variation and Its Causes in A. tigrinmn 35 



the same peculiarity when, by hght feeding during late summer 

 and fall, I have induced them to pass through the winter without 

 metamorphosis. I should add that here again, as in the case of 

 slender bodies and long tails, extremely low nutrition, producing 

 a minimum of growth, does not develop the character. 



Morphologically, this delicate character is not due to a modi- 

 fication of the skeletal structures of the muzzle. This does not 

 seem to be usually the case with amphibians 'which show similar 

 muzzles. It consists, in A. tigrinmn, almost entirely in a growth 

 of the tissues about, and especially above, the external nostril. A 

 kind of supranaral fold develops, forming a somewhat funnel- 

 shaped opening to the nostril, which latter seems also to be en- 

 larged. The cause of this trifling, yet unique, development is by 

 no means plain. Yet there are certain facts, which are interest- 

 ing for themselves, which throw some light upon it. As to the 

 increase in the size of the nostril, this seems to be, frequently at 

 least, a direct result of starvation or of development under very- 

 low nutrition. The same effect may take place during metamor- 

 phosis. It is plainly an instance of tissue-absorption, just as are 

 many other changes about the head, e. g. the reduction of the 

 membranes about the mouth, leading to a great increase in the 

 gape. 



The development of the projection about and above the nostril 

 is, however, plainly of an opposite character. I deem it to be due 

 to an increase in the use of the nostril for the passage of water 

 in the function of pharyngeal respiration. Pharyngeal respira- 

 tion has not, to my knowledge, been recorded as occurring in 

 branchiate amphibia, but I find it present, despite their spectacu- 

 lar gills, and it may be easily demonstrated.^ Moreover, in these 



^I may here add a note on the matter of pharyngeal respiration in 

 A. tigrinum both larval and adult. The fact of the former is surprising 

 and adds one more to the alreadj' bizarre array of facts on amphibian 

 respiration. 



In the American Naturalist for July, 18S9, O. P. Hay notes, in an article 

 "On Some Habits of Some Amblystomas," the fact of pharyngeal respira- 

 tion in the adults of three species of amblystoma, A. microstomiim, A. 

 punctatum, and A. tigrinum. I have confirmed his observations on A. tig- 

 rinum with, however, certain differences. Thus I find the period of these 

 respirations to be very close to ten seconds when the animals are quiet ; 



231 



