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SUMMARY OF CURRENT RESEARCHES RELATING TO 
of the mouth ; and if very considerable use be essential to the maintenance 
of elaborate structure, then we might expect, on the one hand, that the 
teeth in the gill-rakers of the hake should be of very simple structure, 
which is not the case, and, on the other hand, that the large teeth of 
Uraleptus , which must be held to be important in function, and so to 
receive the stimulus of use, should not have lost the structure typical 
for the family.” 
True dentinal tubes are not met with in the Gadidae. The spear- 
point enamel is always present, even upon the smallest teeth. The 
vascular canal system is found in its highest development in those 
members of the family which have the largest teeth, either fixed to the 
jaws by anchylosis (ling, some of the teeth of the hake) or by a highly 
elaborated hinge (the hinge-teeth of the hake). Those which have the 
teeth small in relation to the size of the animal, as happens in a large 
number of Gadidae, and those in which the teeth are not very firmly 
attached, show also a simplification of the minute structure of the teeth. 
But mere smallness of size does not necessarily involve simplification 
of structure, nor large size elaboration. On the other hand, large and 
small teeth in the same creature present identical structure ; and whilst 
the differences in tooth-structure in some instances follow the lines of 
• i lie accepted classification of the genera, in others they do not. 
c. General. 
Problems of Marine Metabolism.* — Prof. K. Brandt, in his rectorial 
address, directs particular attention to two results of plankton-studies. 
The first, that the plankton is more abundant in shallow than in deep 
seas, he interprets on the supposition that in the latter the quantita- 
tive distribution of the essential chemical elements falls below the 
minimum owing to the enormous area involved. The second, that the 
plankton is more abundant in arctic than in tropical or sub-tropical seas, 
he interprets on the supposition that the low temperature hinders the 
action of the de-nitrifying bacteria, which so to speak waste the nitro- 
■ genous supplies in the warmer waters, where they flourish more abun- 
dantly. The address is a very interesting one, and exceedingly appro- 
priate to the occasion, since the University of Kiel is famous as a centre 
of plankton-work. 
Natural Selection and Mimicry. f — Prof. E. B. Poulton has very 
carefully discussed the thesis that natural selection is the source of 
mimetic resemblance and common warning colours. The resemblances 
of mimicry and common warning colours have certain salient features 
in common, certain peculiarities which are apt to manifest themselves 
"repeatedly; they also bear certain general relationships to other resem- 
blances in organic nature. In this paper Prof. Poulton has attempted 
to set down all the general statements which can be made as to the 
phenomena under discussion. These general statements represent an 
enormous number of observed facts ; and on any theory which is not based 
upon selection, the whole of the facts upon which the generalisations 
rest become mere coincidences, and receive no explanation of any kind. 
* ‘Ueber den Stoffweclisel im Meere,’ Kiel, 1899, Svo, 36 pp. 
f Jouro. Linn. isoc. (Zook), xxvi. (1898) pp. 558-612 (5 pls»). 
