270 THE ZOOLOGIST. 



there are certain highly important features in which they do not 

 agree. There is the syrinx ; there is the skeleton, with the 

 marked difference in the proportions of the ribs to the sacrum 

 and the breastbone, and in the fact that while the hinder margin 

 of the latter bone has two notches in the Common Snipe, it has 

 four in the Jack. In the Jack- Snipe the tail has invariably ten 

 feathers ; in the Common Snipe the number, normally fourteen, 

 varies from twelve to sixteen, and their shapes are entirely 

 different. The two species show tremendous differences in voice, 

 breeding range, temperament, flight, and phylogenetic development, 

 and this dissimilarity extends in a lesser degree to the skull, bill, 

 feet, food, and digestive organs. 



Turning back to the main points of resemblance, we shall 

 find that these are all special features fitting their owners to a 

 particular habitat. Both live under much the same conditions, 

 and for this life they require a special bill, foot, long inner 

 secondaries, specially situated eye and ear, and a protective 

 livery. It is perfectly clear that all these features would be 

 acquired sooner or later by any bird living under similar con- 

 ditions. They should not be used for purposes of classification. 



We can take, now, for clearness sake, a single one of the 

 details of internal structure in which the two birds differ, and I 

 think the best feature will be the sternum. This bone is, geneti- 

 cally, built up from the ribs, and during development it throws 

 out lateral and posterior processes which partly enclose the 

 well-known "notches" so conspicuous on the hinder margin. 

 Now, the Common Snipe has two of these notches, the Jack has 

 four. They are absolutely structural characters, and are assuredly 

 indications of the lines on which the sternum has developed. 



For argument's sake we will assume that the two birds are 

 really related, and throughout their entire history have never been 

 farther apart, systematically, than they are to-day ; and this is 

 only another way of saying that they belong to the same genus. 

 Yet, while remaining alike to all outward appearance, the in- 

 ternal skeleton has been undergoing tremendous changes. With- 

 out giving any external signs the Jack- Snipe has grown a second 

 pair of intermediate lateral processes, enclosing an additional 

 pair of notches. Why ? I cannot imagine even a fantastic 

 explanation. 



