118 NATURALISTS’ ASSISTANT. 
or one side of the skeleton may be broken in. olothurians 
should be first carefully examined, and the genital opening, 
which is near the mouth, found. This genital opening should 
be placed in the mediar line above, and then a longitudinal 
incision made from the genital pore to near the anus. This 
will expose the viscera and the parts will show a bilateral 
symmetry. The relation of the longitudinal nerves and 
canals, and the ambulacra should be studied by cutting 
through the integument and one of the longitudinal muscles. 
Clams are dissected by removing one valve. In order 
that uniformity may be obtained the valve removed is the 
left one. ‘To ascertain the right and left, hold the clam with 
the hinge from you, and the end from which the siphons ex- 
tend at your right hand ; the upper valve will then be the left 
one. Insert a dull knife in the gape of the shell and cut the 
strong muscles which hold it closed. These will be found in 
the claea near the hinge line, at the two ends of the shell. 
In the mussel (A7v@7vs) and the oyster but one such muscle 
will be found. ‘The heart (near the hinge line), the aliment- 
ary canal with its tortuous course and the nervous system 
may be then studied. ‘The gills under the microscope show 
a fine example of ciliary action. 
Snails should be extracted from the shell, by breaking it or 
otherwise, and opened from the dorsal surface. 
The larger worms may also be opened from above, but 
many of the smaller ones, especially among the lower forms, 
must be studied in sections. 
Lobsters are opened by removing a portion of the carapax 
exposing the circulatory apparatus, etc. The nervous system 
