1896.] MAilMALIAif DENTITION. 559 • 



represented in one set, belong to the replacing series, being pre- 

 ceded by tooth-vestiges referable to the milk-dentition. This last 

 conclusion I can now entirely confirm and strengthen, for the 

 specimens which I have investigated exhibit these features much 

 better thau Leche's embryos did '. 



Both Leche and myself have investigated Erinaceus, Ericulus, 

 Sorex, and Talpa, and he has further studied Crossopus, Scalops, 

 and Condylura, whilst I have independently investigated Centetes 

 and Gymnura. These are unfortunately representatives of only 5 

 out of the 9 families of living Insectivora (Flovvfer and Lydekker, 4), 

 thus leaving at least 4 other families, some of which are extremely 

 interesting, still to be investigated. 



In addition to studying the relations of the two sets of teeth, 

 I have attempted to trace the origin of the cusps of the molar 

 teeth, noting especially the order of development of those struc- 

 tures in the light of the researches of Osborn, Eose, and Taeker. 



EeINACEUS ECEOPjEUS. 



Of our common English lledgeliog I bavQ examined two speci- 

 mens intermediate in age between Leche's stages E and P, that is 

 between his oldest foetus aud his new-born young. Further, I 

 have examined a large series of dried skulls, including those in the 

 collection at the British Museum. 



The statements concerning the milk-teeth of this genus and 

 allied forms in many, especially the older, text-books are most mis- 

 loading, and even in more modern works we find the whole group 

 described as diphyodont. This, though strictly true, was not based 

 on any detailed examination of the various genera, but rather 

 hastily concluded from the knowledge that one form was found to 

 exhibit tliis condition, or else copied from some old and unreliable 

 accounts, as, for instance, tliat of Eosseau (21), who stated that 

 Erinaceus had a deciduous dentition composed as follows, viz. : — 

 i. f , pm. ^, which were shed at the age of 7 weeks. Dobson (3) 

 also speaks of a full milk-dentition, but it is obvious that he simply 

 described as milk-teeth all those teeth which were visible in the jaw 

 of the youug Hedgehog at birth, and that he had never seen any 

 actual replacement. He states, in contra-distinction to Eosseau, 

 that at 6 weeks all the permanent teeth were present. 



The erroneous nature of these conclusions has been pointed out 

 by Leche (9) ; and it may be ascertained by anyone, from the study 

 of a few young skulls, that the only milk-teeth recognizable by tho 

 ordinary methods of dissection or examination of dried skulls are 

 i. f-, c. (^), pm. f . The remainder being only to be made out, and 

 then with dilUculty, by the examination of serial sections of fcetal 

 jaws, a method not adopted by the earlier observers. 



' It is just possible that our English Iledgehoe difTera iu respeot to tho 

 uiuouut of devefopnient of tliese iniik-tooth vcdtiges Irom its (iontiiienlal cousin, 

 although they are coiitidered as one species ; on the other hand, my two speci- 

 lut^iis may represent individual variations. 



