30 
Address of the President. 
of Nature ;" and 1 should be the last to attempt to set up as 
fixed laws what are merely the expressions of the present state 
of our knowledge, or to wish to throw discredit on the ob- 
servations of accomplished and careful microscopists, merely 
because they overthrow distinctions which I had imagined to 
be well founded. I would strongly recommend the observa- 
tions of Professor Hartig (Quart. Journ. of Microsc. Science, 
Vol. IV., p. 51) and of Mr. Carter (Ann. of Nat. Hist., Feb., 
1856) to your attentive scrutiny ; and hope that some of our 
members may be able, ere long, to furnish either a confirmation 
or a refutation of them. 
Turning, now, to some of those parts of the fabric of higher 
animals, in which a cellular organization has been described 
by some observers and denied by others, I think I shall be 
able to show that the discrepancy is capable of being recon- 
ciled, by the application of the principle of progressive dif- 
ferentiation to the mass of sarcode in which any such organ 
originates. Thus having found, in various kinds of shells, 
certain instances in which a very definite cellular organization 
appeared to me to exist, — others in which this organization 
was less definite, though still (as I thought) unmistakeably 
present, — others in which it was only faintly indicated, — and 
others in which I could discern no traces of it ; — and having 
also met with gradations from one condition to another, even 
in the very same shells ; — I thought myself justified in con- 
cluding that the animal basis of the shell-substance must have 
been originally cellular in every case, but that the divisions 
between the cells must have been lost in some cases by a very 
early coalescence. Mr. Huxley, on the other hand, has recently 
expressed an opinion,* founded on an examination of my own 
preparations, that the whole of my interpretation is erroneous, 
and that no cellular structure can really be discerned in shell. 
Now in the justice of this verdict, I cannot say that I am pre- 
pared to coincide ; on the other hand, I am quite ready to 
admit that my original interpretation requires modification. 
Taking the general history of the first formation of a leaf from 
a layer of protoplasm, as probably applicable to the formation 
of a lamina of shell from a layer of sarcode, I should now 
interpret the appearances which my preparations exhibit, as 
follows : — In those forms of shell-substance in which I can 
discern no structure whatever, and in which a continuous 
membrane is left after decalcification, I should be disposed to 
think that the entire layer of sarcode has undergone calcifica- 
tion, before any differentiation of parts had begun to take place 
in it. In those again in which (as in Mya and Thracid) a 
* * Cyclopcedia of Anat. and Physiol.,' Supplement, p. 489. 
