254 
POPULAR SCIENCE REVIEW. 
EXPLANATION OF PLATE. 
Fig. 1. From a drawing made from a specimen of Anodonta Cygnea 
• dissected by tbe author. 
The valves of the shell have been separated wide apart, in 
order to display the contained animal and certain markings on 
the interior of the shell. This can be done with moderate ease, 
by passing the handle of a scalpel between the mantle and one 
of the valves, and afterwards, with the blade of the instrument, 
gently cutting through the two adductor muscles close to their 
attachment to the valve (a a' and/) a'). By bending back the 
freed valve with moderate force, the resistance of the hinge can 
be overcome without any damage resulting. All further exa- 
mination of the animal ought to be made under water or dilute 
spirit. 
It has been attempted in this figure to show as much as 
possible, with the least possible disturbance of parts. The 
animal is left lying in situ , resting on its right side, in the right 
valve of the shell. The right mantle-lobe (m) is quite undis- 
turbed, except slightly at the anterior end. The posterior half 
of the left lobe (m') has been slightly drawn aside, while the 
anterior half has been completely turned outwards, so as to 
display the deeper parts of the animal, as also its own thinner 
portion (to which the letter m:' points) which secretes the 
nacre, while the thicker 11 collar,” to which the growth of the 
shell is due, is seen at its posterior half. The transverse 
prominence ( a a) at the anterior end of the animal, where the 
mantle-lobes join, is caused by the underlying anterior adductor 
muscle, whose cut extremity is concealed by the overlapping 
left mantle-lobe, while that of the posterior adductor (p a ), and 
of the posterior retractor of the foot (r p p), is seen projecting 
from the thin portion of the same lobe, at its posterior end. 
At the posterior part of the right lobe are visible the fringes 
which project from the inner wall of the rudimentary siphon ($). 
Next to the mantle come the two pairs of gills ( rg,rg,lg , Ig ), 
which are left nearly undisturbed ; the outer one on the left side 
has, however, become somewhat contracted. Only a portion of 
the outer right gill is visible. The tongue-shaped body marked 
F is the foot ; it is much contracted, and, though somewhat fore- 
shortened in the drawing, is turned to the right, so as to show 
its edge and left side. The triangular opening (m), situated 
betwixt its anterior extremity and the prominence caused by the 
anterior adductor, is the mouth. On either side droop, like 
curtains, the leaf-shaped double tentacles (r t , It ) ; the inner 
leaflet of each joining its fellow over the root of the foot to form 
the posterior boundary of the mouth. Only a part of the right 
tentacle, the outer leaflet, is visible ; that of the left tentacle is 
slightly turned over at the edge, so as better to bring into view 
