The Lateral Nasal Glands of Amphiuma. 167 



The larger number and greater extent of such tubules in Amblys- 

 toma as compared with their very limited development in secondarily 

 aquatic forms such as Diemictylus emphasizes the association of their 

 function with aerial respiration under terrestrial conditions ; and 

 their complete absence in the aquatic forms, liecturus, Siren, and 

 Cryptobranchus, adds further corroboration. That the secretion of 

 these glands, or of their homologues, may come to subserve, second- 

 arily, a more specialized function, I have showm elsewhere in the case 

 of the naso-labial group of glands of the Plethodontidae and Des- 

 mognathidse, but the primary function seems certainly to be this 

 more generalized one of protecting the delicate skin of the crescentic 

 fold from the drying effects of the atmosphere. 



Here Proteus seems to be an exception, for it is a wdiolly aquatic 

 form which possesses external nasal glands. Their rudimentary 

 nature must be remembered, however. This fact show^s that what- 

 ever the environmental condition may have been to which the glands 

 were an adaptation, this condition no longer exists. If, as seems 

 probable, this condition was one of terrestrial life, the present form 

 must be looked upon not as primitive, but as either a degenerate form 

 or a permanent larva. The absence of nasal muscles is quite in 

 accord with either view. 



Turning now to Amphiuma, we find ourselves confronted by the 

 problem of external nasal glands which have not only reached a high 

 degree of complexity of development, thus bearing witness to the 

 importance of their function, but which in their development have 

 concentrated their secretion at a single point, although they begin 

 tlieir development as do the external nasal glands of other urodeles 

 as several separate tubules. To explain the special function which 

 this glandular mass has in Amphiuma I have considered in what 

 respects the needs and adaptations of Amphiuma differ from those 

 of other urodeles, and have directed my observations along those lines. 



In habit the Amphiuma is teri'estrial as well as aquatic. Even 

 under aquatic conditions it spends much of its time burrowing in the 

 mud at the bottom of the water; and in its terrestrial habitat it is 

 described as living in the soft mud and burrowing through it almost 

 like an earthworm. The whole form and structure are well suited 



