600 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
a few pages to tlie accessory optic vesicles the author passes to the 
pineal sense-organs. The evidence appears to favour the idea that the 
pineal sense-organs are multiple, and individually of paired origin. 
There appears to be a distinct relationship between the auditory plane, 
the branchial sense-organs, and the lateral line. 
Mammalian Dentition.* — Mr. M. F. Woodward, in the second part 
of his contributions to the study of mammalian dentition, treats of the 
teeth of certain Insectivora. As may be supposed, Mr. Woodward begins 
with an account of the dentition of the common hedgehog. It would 
appear that, in the only living mammals believed to possess unmodified 
trituberculate teeth (molars and posterior pre-molars), wdiich have been 
examined developmentally, the order of cusp ontogeny is in entire 
accord with the supposed order of cusp phylogeny, as advanced by the 
supporters of the Cope-Osborn tritubercular theory. This is a very 
striking and important fact. 
Mr. Woodward comes to the conclusion that the antero-external cone 
is the primitive, both in the molars and pre-molars. The protocone is 
borne on an internal shelf of secondary origin. The metacone is a 
similar backward development of the paracone, rising very early, long 
before the protocone. The hypocone stands related to the metacone, 
as the protocone does to the paracone. Mr. Woodward thinks that the 
evidence advanced in support of the tritubercular theory is insufficient to 
prove that the upper molars were primarily evolved on the lines of that 
theory. Owing to want of material, trituberculists have been led to 
assume that the upper molars of the early Mammalia pass through 
similar stages to those which they have determined for the lower teeth, 
and consequently they have, in most cases, incorrectly identified the 
primary cone. As regards the primary cone its ontogeny recapitulates 
its phylogeny. If it be a fact, as is now generally believed, that the 
milk dentition preponderates in the early Mammalia and in the living 
Marsupials, we must come to the conclusion that the living Insectivora 
are specialised forms, tending towards a monophyodont condition, in 
which the preponderating dentition is the replacing or permanent set. 
Teeth of Marsupials. t — Mr. M. F. Woodward has made a study of 
the teeth of marsupials with special reference to the pre-milk dentition. 
He points out that recent investigations concerning the ontogeny of the 
mammalian dentition have completely revolutionised our conception of 
the tooth succession in this group. From a belief in the primitive nature 
of the monophyodont condition of many mammals, we have been led to 
see that this is a secondary condition derived by reduction from a 
diphyodont stage. Still more recent research proves that we must 
regard all mammals as potentially polyphyodont, and possessed of traces 
of four or five dentitions : firstly, there is the pre-milk dentition ; 
secondly, the milk ; thirdly, the replacing or permanent dentition ; and, 
fourthly, the post-permanent which is often described as the third 
dentition. 
For some years past Mr. Woodward has been working at the poly- 
protodont marsupials, and has found a set of minute teeth present in 
* Proc. Zool. Soc. Lond., 1896, pp. 557-94 (4 pis.). 
f Anat. Anzeig., xii. (1896) pp. 281-91. 
