1901} MICROSCOPICAL JOURNAL 285 
alternate contraction of two sets of muscles, protractors 
and retractors, attached at one end to the base of the cush- 
ion and at the other to the radula, the latter is dragged 
backwards and forwards over the cartilaginous pad, as an 
ostler polishes the inside of fixed rings by pulling a cloth 
to and fro within. Listen to the limpets as they rasp 
slowly over the rocks, and you will understand clearly 
how effective is this radula in scraping off minute vegeta- 
tion that coats the rock. The sound given out is too def- 
inite to be mistaken. The scraping action of the radula 
is also very easily studied in a fresh-water aquarium con- 
taining a few water-snails. As the teeth in front wear 
down, the ribbon is bodily moved forward sufficiently to 
permit new teeth to come into use.” Then follows a de- 
tailed description of the teeth and of the classification. 
From notes accompanying a miscellaneous set of slides 
we extract the following remarks on a slide showing the 
prismatic raphides in the cuticle of an onion. (Allium 
cepa): “Lime enters largely into the composition of all 
organic bodies. In human bones, for example, the salts 
of lime constitute 65 per cent of the whole mass, or more 
than double the amount of animal matter. There are very 
few plants in which these limey crystals or raphides are 
not found. They vary considerably in size and shape, and 
itis by no méans difficult to detect them by cutting thin 
sections of plants and examining them under the micro- 
scope. A glass slip, a cover-glass, and a little water are 
all the mounting materials necessary. They will not, of 
course, come out so clearly as in a slide made by a pro- 
fessional mounter ; but it is always interesting to do some- 
thing for oneself, and facts observed in this way are firm- 
ly impressed on the memory. The simplest form of raph- 
ides is to be found in the lilies, where these bodies occur 
in the form of bundles of needle-like rods occupying the 
centre of the cell, In the strip from the outside of a lily 
stem they areseen under an inch as an almost solid mass in 
