Mammalia. 57 



they occur, however, with much completeness in certain teeth taken 



2 

 througliout the series, such as premolar— of either jaw, and I have 



nut the slightest doubt that in a series of sufficient size they would 

 be exhibited in every cheek-tooth. 



(IX.) It seems fair to regard this variability of the rooting as 

 closely connected with the actual reduplication of the teeth, so 

 that a tooth with double roots would, perhaps, in this species, be 

 regarded as no less on the way to reduplication than a tooth witli 

 double crowns. At all events this possiliility is strongly sug- 

 gested by tlie numerous intermediate steps which occur between 

 a tooth with a single columnar root and a fully double-rooted 

 tooth. 



(X.) This variability in respect to the roots is not confined to the 

 original teeth, but may occur also in the supposed " daughter " teeth. 

 A pair of these may occur in any of the following combinations : — 

 (a) both single-rooted ; (/3) both double-rooted ; (7) ^ one double- 

 rooted and the other single-rooted ; or (8) one fully, and the other 

 only partially double-rooted. Further, a single-rooted pair of 

 " daughter " teeth on one side of the jaw may 1 )e represented by a 

 double-rooted pair on the other side, as in No. 4. 



(XI.) The variability in respect to the roots is greater in some 

 teeth than in others. Thus (although one or both of the " daughter " 



teeth of m. — • may be single-rooted), in no head except No. 3 



does this tooth itself, if unreduplicated, possess less than two roots. 

 Where reduplication is supposed to have occurred, one or both of the 

 " daughter " teeth may be single-rooted. It is remarkable that the 



only instance of a single-rooted m, — - is due, apparently, to a case 



of "sympathy." This occurs in No. 3, a head in which both 



,,1 4 



"daughter " teeth of m. — are single-rooted. Similarly, p.m. — , although 



very variable in the nature and development of the two roots, only 

 once appears (in No. 324^), with a single flattened and grooved 



root, while p.m. -j- is never single -rooted. P.m. — and -^ appear 



2 

 each once single-rooted (both again in No. 324&). P.m. — and -^ 



each appear twice, with single roots, and to these exceptions No, 324& 

 * Cases y and S occur opposite to each other in the same jaw. 



