1893. NOTES AND COMMENTS. 7 
on etymological grounds, but were used with too great laxity. As now 
revised, the technical terms are as follows :—embryonic, brephic (= in- 
fantine or larval), neanic (= adolescent), ephebic (= adult), and gevontic 
(= senile), the last being subdivided into catabatic (= declining) and 
hypostvophic (= atavic). These terms are restricted to stages in the 
growth of an individual. By prefixing the syllable phy/- they may be 
made to express stages in the history of a race; while the successive 
stages in the evolution of a character may be designated by the 
same terms with the addition of the prefix morpho-. Confusion of 
terms leads most surely to confusion of thought, and if the latter be in 
any way dispelled by the labours of Messrs. Buckman and Bather, we 
are bound to be grateful. 
THE GROWTH OF SHELLS. 
A most peculiar, and, as far as is at present known, unique mode 
of increase in a Gastropod shell, is described by Mr. B. B. 
Woodward in the last number of the Pvoc. Zool. Soc. London (1892, 
pp. 528—540, pls. 31, 32). Broadly speaking, the Gastropod shell 
may be looked upon as a more or less elongate conical tube, at the 
apex of which is the young shell, while increase takes place by the 
addition of fresh material at the other, open, extremity—the mouth. 
This tube is usually spirally coiled in the direction of a screw, the 
successive whorls touching one another. In those forms where the 
spire is low and the whorls are close together, the portion of the 
tube next the previously-formed whorl is sometimes largely, some- 
times completely, dispensed with, and what was in the first instance 
the outermost wall of the tube becomes in the course of growth the 
dividing partition between the last whorl and its predecessor. When 
the shell is a very thick one, the presence of an equally stout 
internal partition (pavies) between the whorls becomes unnecessary, 
and even inconvenient; hence it is very frequently to a great extent 
re-absorbed and reduced in thickness by the animal, as, for example, 
in Conus. 
The Neritidze advance a step further, and usually remove the 
greater part of the paries altogether, converting the shell into a 
single chamber, the only remnant of the dividing wall left being a 
portion near the mouth, to which one of the retractor muscles 
is attached. On the other hand, this remaining fragment of 
paries is usually strengthened, sometimes considerably, by an extra 
layer of shelly material. In extreme cases this deposit forms an 
independent projecting shelf (septwm), standing out from the paries 
into the general cavity, between the former and the mouth of the 
shell. In these instances the septum forms the point of attachment 
for the retractor muscle, and the remnant of the paries is reduced to 
insignificant proportions or disappears entirely. The different species 
of Nevitina and Nerita exhibit the various stages in the process. 
