SPONGES 5 
EESSONAON, SRONGES. 
The following is, in a measure, a summary of the fore- 
going in the form of a lesson, which, although intended for 
pupils from the higher grade of a grammar school, to those 
of high and normal schools, may be adepted by simplifying, 
to lower grades. 
A sponge is an animal, fixed when adult, composed of 
a soft outer covering in which life and motion abide, and 
which answers to our flesh, and consequently, from a scien- 
tific point of view, is the most important organisms tostudy. 
and is usually provided with a hard skeleton, which is of 
rather less importance, 
Show a sponge with flesh and a hard skeleton; the or- 
dinary sponge of commerce. 
Although not quite natural, it is usual to divide spong- 
es into two groups, Horny and Spiculigenous (for final 
arrangement, see Classification of Sponges. ) 
We will first consider the Horny Sponges. 
