1896.] MAMMALIAN 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 than Leche’s embryos did *. 
Both Leche and myself have investigated Hrinaceus, Ericulus, 
Sorev, and Valpa, 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 (Flower 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, Rése, and Taeker. 
ERINACEUS EUROPEUS. 
Of our common English Hedgehog I have examined two speci- 
mens intermediate in age between Leche’s stages E and F, that is 
between his oldest foetus and bis new-born young. Further, I 
haye 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- 
leading, 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 this condition, or else copied from some old and unreliable 
accounts, as, for instance, that of Rosseau (21), who stated that 
Erinaceus had a deciduous dentition composed as follows, viz.:— 
i. 2, pm. 4, 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 young Hedgehog at birth, and that he had never seen any 
actual replacement. He states, in contra-distinction to Rosseau, 
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 oniy milk-teeth recognizable by the 
ordinary methods of dissection or examination of dried skulls are 
i. 2, c. (1), pm. ?. The remainder being only to be made out, and 
then with difficulty, by the examination of serial sections of foetal 
jaws, a method not adopted by the earlier observers. 
1 It is just possible that our English Hedgehog differs in respect to the 
amount of development of these mitk-tooth vestiges from its continental cousin, 
although they are considered as one species ; on the other hand, my two speci- 
mens may represent individual variations. 
