MESOTANIUM, AND SPIROTANIA. 223 
pose—be the intermediate phases what they may—that these 
would naturally begin and end their cycles in themselves, 
than that all the many well-defined types and well-marked 
forms, some more and some less frequently recurring, in- 
cluded under ‘“‘ Palmellaceze,” should need constant recruiting 
by the transmutation of lichen-gonidia and moss-spores. 
Perhaps the truth on some of the questions lies in the mean ; 
but, be it as it may, I trust I am not too firmly attached to 
the views I have tried to express not to relinquish them on 
good evidence. Meantime, in the words of Dr. Wallich, I 
at least hold with him, that—“ In science, as in governments, 
truth can never be arrived at on a large scale unless under 
the pressure of an opposition.” 
Mr. W. Archer prefaced the foregoing paper by reading an 
extract from a letter addressed to him by Dr. G. C. Wallich, 
F.L.S., on the subject of the value of characters in Proto- 
phyta, more especially in Desmidiacee. Mr. Archer ex- 
plained that Dr. Wallich’s remarks therein were in reply to 
observations of his own in a paper read before the Natural 
History Society of Dublin on the 4th of December, 1863, 
entitled ‘Observations on Micrasterias Mahabuleshwarensis 
(Hobson), and on Docidium pristide (Hobson) ;’* and that 
Dr. Wallich, having done him the honour to write him a 
letter containing a summary of his own views on the subject 
debated in the paper referred to, had requested him to read 
the same to the Natural History Society. The following is 
the extract, reference to which is made in the preceding 
paper : 
“Pray do not for a moment think me inclined to take 
amiss any differences of opinion on scientific matters. Every 
one has a right to judge for himself; and in science, as in 
governments, truth can never be arrived at on a large scale 
unless under the pressure of an opposition. Besides, the 
question of specific limits is still in its infancy; and those 
who cling to permanent specific types are most fully justified 
in crying out for the amplest proofs before relinquishing 
their ground. You know of old that I am for no such per- 
manence, but believe that I can trace at every step more and 
more conclusive evidences that there exists a constant 
tendency to modification by external influence. 
“The point at which you and I diverge is that at which 
we form our estimates of the value of characters. You 
maintain that certain characters, hecause they are more or 
* ©Proceedings of the Natural History Society of Dublin, vol. iv, Part 2, 
p. 79. 
