870 Dr Yule on the analogy of the organs of the Embryo 
that they belonged to the Zeolite Family. Having purchased 
all the specimens that could be found, I have since repeatedly 
examined the included crystals, with the view of determining 
their nature. I found that they did not belong to the zeolites, 
but consisted principally of carbonate of lime ; and, as every 
mineralogist who saw them considered them as something new 
in appearance, I expected that a greater quantity of them might 
be found for the purposes of analysis. Familiarised, therefore, 
with the aspect of these groups, I was convinced that the crys- 
tals in the fluid cavity were the same substance; and a more ac- 
curate examination has established their perfect identity. 
These white crystals sometimes occur in minute insulated 
spiculae within the solid mass, but most frequently in spherical 
groups of extreme beauty, surrounded with the most transparent 
quartz. Many of the open hollows and crevices of the quartz 
crystals are filled with them, and numerous aggregated groups 
adhere to their external surface. These crystals, though very 
minute, I have found to have a powerful double refraction ; and 
as they are wholly dissolved with effervescence, excepting a little 
adhering silex, in diluted nitric acid, there can be no doubt that 
the external crystals, and consequently those in the fluid cavity, 
are carbonate of lime *. 
Art. XIII . — Observations on the presumed Analogy of certain 
Organs of the Embryo , in several distinct Races of Vascular 
Plants. By John Yule, M. D. F. B. S. E. Fellow of the 
Royal College of Physicians, Edinburgh. 
P revious to entering on the detail of the facts, on which the 
following conclusions are founded, whether true or false, I may 
be permitted to state, that, in all our inquiries after truth, there 
is nothing of greater moment than an accurate and definite use 
of terms : for it is probable, that the neglect of this, more than 
any other cause, has retarded the progress of the sciences in ge- 
neral. Words used in a loose or improper sense, indeed, do 
worse than retard : they bewilder and mislead, by substituting 
* Since these observations were made, Mr Nordenskjold has confirmed this re- 
sult, by experiments made with the blowpipe. 
