148 
Transactions of the 
TMonthly Microscopical 
L Journal, March 1, 1869. 
with great practical knowledge. This paper will be found in the 
* Monthly Microscopical Journal ' for February, and deserves to be 
attentively studied by all who are engaged in the arrangement of 
collections. 
On the same day Dr. CoUingwood described a curious micro- 
scopic alga colouring the sea in various parts of the world, and 
especially in the China Sea. This curious plant gives the water 
"a dusty appearance," as though myriads of minute bodies were 
floating upon the surface and at various depths below. In some 
instances "a cream-coloured pellicle " would cover the sea for nearly 
the whole day with little interruption. These appearances were 
occasioned by minute bundles of vegetable filaments jointed like 
Confervae. Dr. CoUingwood describes some other floating bodies, 
but he did not encounter the " blood-red algae," which seem to have 
been nowhere met with but in the Bed Sea and in the Arabian 
Gulf, and only occasionally in those localities. 
In April, Mr. Hogg read a paper, accompanied by many 
beautiful drawings of the Lingual Membranes of the MoUusca, 
and their value in classification. To Professor Loven, of Stockholm, 
we are indebted for the first attempts to make the lingual membranes 
a means of description. He proposed to divide them into fourteen 
groups, and separated the genera into families and sections charac- 
terized by the number, position, and forms of the teeth. This 
arrangement appears to have received the approval of Dr. Gray, 
Dr. Troschel, and others, who have sought to extend it and form it 
into a reliable basis for distinguishing species. The late Dr. J. C. 
Woodward appears not to have had much confidence in the system- 
atic value of the lingual membrane, for he observes : — " It must be 
remembered that the teeth are essentially epithelial cells and, like 
other superficial organs, liable to be modified in accordance with the 
wants and habits of the creatures." This is true to a certain extent, 
but if, as Dr. Macdonald remarks, it is intended by the assertion 
that the teeth are essentially epithelial cells, to lessen their morpho- 
logical importance and convey the idea of mutability, surely we ought 
to be able to draw a distinction between the normal and abnormal 
development of the same organs in different members of the same 
species. Moreover, the teeth are formed from a special matrix at 
the fundus of the lingual sac, determining in every case the constant 
evolution of certain characters ; any defect in the formative pulp 
will repeat any consequent formation in each succeeding row of 
teeth. Notwithstanding the remarks just cited. Dr. Woodward must 
have seen some value in the lingual classification, for he proceeded 
to arrange his cabinet of so-called " palates " upon this system, and 
it was Mr. Hogg's good fortune to be able to draw upon this collec- 
tion for the valuable and beautifully executed series of plates which 
adorn the pages of our transactions. 
