180 HERAPATH, ON THE 
potash, shortly the musculo-membranous indusium becomes 
transparent, if not dissolved; and all the calcareous elements 
become apparent, but still not sufficiently clear for photo- 
graphic purposes. Under these circumstances it is necessary 
to boil up each animal in distilled water containmg a 
tolerable quantity of caustic potash, which dissolves all the 
fleshy coverings, and the calcareous pieces are made clean 
and transparent. In many instances, if the boiling has been 
carefully stopped at the proper time, the two or three blades 
constituting the forceps-like appendage remain in conjunc- 
tion, and are then very much more instructive preparations 
to the microscopist. In order to remove these pedicellarize 
from the other calcareous débris of the Echinoderm it is 
necessary to allow all matters to subside and decant the 
supernatant alkaline solution ; and, having removed all traces 
of potass by frequent washings and subsidence with successive 
portions of distilled water, it only remains to agitate the 
whole well together with a steady circular’ motion, and after 
some moments’ repose pour off the supernatant water which 
contains the pedicellarial blades in suspension. On repose 
these subside, and may be then removed by a dropping tube, 
placed onaslide, dried, and mounted in Canada balsam in the 
usual way. 
The objects now exhibited in photographs have all been so 
prepared by the author himself, and are, consequently, 
authentic specimens, and have all been photographed to one 
scale for comparison with the same lens and camera. They 
are under the same identical circumstances in each particular 
case, so that relative size may be taken into consideration as 
one of the elements of difference. 
The objectives used were a Ross’s inch and half-inch, two 
beautiful lenses, in which the visual and actinic foci rigidly 
corresponded, which of course contributed much to the 
beauty of the photographic pictures, the absolute accuracy of 
which is only limited by the degree of penetration of the 
lens. Direct solar light has been in all these micro- 
photographs an absolute necessity; the image of the sun 
being actually necessary to the formation of an image possess- 
ing the intensity requisite for photographic printing purposes. 
A general view of the pedicellariz of an animal was first 
taken with the inch, giving about twenty diameters ; then each 
form of pedicellarial blade was separately taken with the half- 
inch, giving a magnifying power of fifty-five diameters. 
As this paper is still far from complete in the determina- 
tion of many points of great interest for the coming sections, 
the author would feel deeply indebted to any reader who would 
