APPENDIX. 
411 
of sponges is difficult for the beginner. The arrangement of 
the canals and the microscopic structure of the skeleton of the 
Toilet Sponge should be studied (Fig. 190). Specimens for 
this work may be purchased at any drug-store. Then alcoholic 
specimens of similar sponges, in which the flesh has been pre¬ 
served, may be sectioned in various directions with a sharp 
knife, and the difference between the skeleton and the complete 
body noted. Sections of Grantia , or of some other simple 
sponge prepared in such a way as to show the canals and ciliat¬ 
ed chambers, as well as the young in various stages of develop¬ 
ment, may be purchased from any dealer in microscopic supplies 
(Fig. 189). 
Ccelenterates.— If the fresh-water Hydra (Fig. 191) can be 
obtained it will be found' useful to illustrate the structure of 
the Coelenterata. It lives in clear water in ponds and ditches, 
and attaches itself to the stems and roots of floating plants, as 
duck-weed, various algae, etc. Either the green or the brown 
form may be used. The animal may first be examined in the 
aquarium, and the movements of its body and tentacles noted; 
also its method of locomotion. Then it may be placed in a 
watch-glass, and studied under the low power of the micro¬ 
scope ; small scraps of fresh meat not so large as a pin-head 
may be given it, and its method of feeding watched. If placed 
on a slide in a drop of water and covered it may be examined 
with a higher power and the structure noted—the body-wall 
consisting of cells arranged in two well-defined layers, many of 
the cells containing green particles; the digestive cavity ex¬ 
tending throughout the body and into the tentacles; from some 
of the cells the nettling - threads may be seen to shoot out. 
Look for specimens bearing buds. Prepared slides showing 
longitudinal and cross sections of the body may be purchased. 
If hydras cannot be obtained, some of the marine hydroids, 
either living, alcoholic, or stained specimens mounted on slides 
should be studied. The campanularian hydroids are suitable. 
These are colonial forms, and in each colony both feeding and 
reproductive zooids will be found, as well as young zooids in 
various stages of development from the first formation of the 
bud to the full-grown zooid. Study live specimens in sea-water, 
noting particularly their movements, and, if possible, their meth¬ 
od of feeding. Examine alcoholic specimens in a watch-glass 
containing fifty per cent, alcohol. Note the plant-like aspect 
