'4:4 - 'Address of the President at the Annual Meeting. 
facts, of the well-known experiments of Dr. W. F. Edwards 
upon the development of the Tadpole, and of the more recent 
experiments of Mr. Higginbottom upon the same subject ; 
-and as there is some difficulty in reconciling these two sets of 
results, I would strongly recommend Mr. Hogg and other 
members of our society to follow up the inquiry, by a more 
extended series of investigations into the circumstances which, 
separately or combined, affect the development of the Lymnceus 
especially the influence of light and temperature, supply of 
food and oxygen, and limitation of space ; the last, I suspect, 
taking effect through the limitation of food and oxygen.* 
Professor Gregory has continued his interesting communi- 
cations upon Diatomacece ; and one of the papers with which he 
has favoured us has a very important bearing upon a question 
which is exciting great interest among really scientific natural- 
ists at the present time, viz., the range of variation within the 
limits of species. For in almost every department, both of 
Zoology and Botany, it is coming to be generally felt, by 
those who have devoted themselves to the inquiry in a truly 
philosophical spirit, that there has been by far too great a 
readiness to establish new species, and to confer new names, 
for the sake of distinguishing forms, which, when more care- 
fully compared, are found to pass into one another by imper- 
ceptible gradations, or to be but different states of the very 
same organism. The time is now, I hope, entirely past, v/hen 
the extent of a naturalist's acquirements in any particular de- 
partment, were estimated by the number of species in his 
collection, instead of by the amount of his knowledge of all 
that concerns them. Yet still we find that what I may desig- 
nate as the mere collector's spirit is far too widely prevalent ; 
* I feel it requisite to take this opportunity of correcting an error into 
which Mr. Hogg has fallen, in alluding to my observations on the struc- 
ture of Shells, and comparing them with those of Mr. Bowerbank. He 
represents me (Transactions, vol. ii., p. 96) as inclining to the opinion of 
Keaumur, who considers Shell an inorganic exudation from the surface 
of the dermis ; whereas the whole aim of my descriptions was to prove 
that Shell is an organized cellular tissue, being, in fact, a calcified epi- 
dermis. It is true that I disagree with Mr. Bowerbank (whose opinions 
Mr. Hogg supports), in maintaining that Shell is not vascular in the ordi- 
nary sense of the term ; that is, is not penetrated by blood-vessels from 
the subjacent tissue. But it no more hence follows that it is not endowed 
with vitality, than that epidermic and epithelial structures, or cartilage, 
are dead or inorganic, because they have no vessels ; and the increase and 
reparation of shell may well take place, like those of the tissues just 
named, at the expense of nutriment brought to it by the vessels of the 
subjacent surface, although that nutriment is not distributed through it 
by the extension of those vessels into its substance. Mr. Hogg appears 
to have laboured under the very common error, of supposing that what is 
non-vascular must necessarily be inorganic also. 
