last has been shown by the late G. K. Noble to throw much light on the re- 

 lationship of species. 



Embryology Since egg-laying can often be induced by pituitary implants, 

 it is possible to follow the embryological development at other times than the 

 normal mating season. Even gross studies are of value. Correlations between 

 temperature and other environmental conditions and the rate of development 

 can be determined. Presence of balancers and their degree of development 

 at hatching time, size and form of external gills, and development of limbs are 

 characters by which one might be able to identify eggs and larvae at different 

 ages. All these should be determined and recorded for each species. 



A survey of the technical characters which separate families and genera 

 of salamanders will reveal that most of the distinctions are based on the skele- 

 ton. If serious study of the group is intended, the student should master the 

 technique of the alizarin bone stain and the potash clearing methods. A brief 

 account of the structural characters used in the key follows. 



HEAD 



The members of one family, Plethodontidae, are unique in possessing a 

 naso'lahial groove running from each nostril vertically to the mouth. On the 

 adult this is plainly visible, since there is no pigment along its course. Its 

 function is apparently to drain the water quickly from the nasal area as the 

 animal emerges from the water, probably a matter of importance to a lungless 

 animal which uses its mouth for respiration (bucco-pharyngeal respiration). 

 Two genera, Desmognathus and Leurognathns, have the lower jaw rigid, the 

 mouth being opened by lifting the upper jaw and head. This stiffness ap- 

 parently enables the animal to push its way more readily under rocks and 

 debris. It also gives the animal a characteristic profile, of aid in identifica- 

 tion. The attachment of the tongue varies in different forms, some having it 

 attached at the front, some at the back, and some with a median attachment, 

 both ends being free. The patches of teeth on the roof of the mouth are also 

 important in taxonomy. The diagrams should be consulted and the location 

 and different arrangements of vomerine or vomer o- palatine and parasphenoid 

 teeth noted. Below the chin a fold of skin, the gular fold, is present in some 

 groups. 



BODY 



Along the sides of the body and tail of many of the salamanders a number 

 of folds or line-like, vertical depressions may be seen. These mark the posi- 

 tions of the ribs and are called costal grooves. The number of these on each 

 side between the fore and hind limbs, including those directly at the point of 

 attachment of the limbs, often aids in determining the identity of a salamander. 



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