98 NEW ZEALAND NATURE-STUDY BOOK 
and where required. If a popular name answers the purpose, 
it is the reverse of wise to make use of its scientific equivalent— 
nothing will be gained for instance by speaking of the leaf-stalk 
as the petiole, or the thigh-bone as the femur. Itis only when 
popular phraseology can furnish no equivalent, as in the case of the 
essential organs of the flower, stamens, pistil, etc., or, where it 
fails in accuracy of expression, or where the scientific name is 
terse, pointed, and easily remembered that it (the technical or 
scientific term) should be employed. 
I].—A SPONGE. 
The common sponge belongs to a division of the sub- 
kingdom Ccelenterata, known as Porifera, or animals 
whose bodies are traversed by canals which open to the 
surface and are connected with a central cavity. 
That a sponge is a porous substance is easily demon- 
‘strated to a class; one has only to place it in a vessel 
containing water, and require pupils to observe the 
disappearance of some of the liquid when the sponge has 
been removed. The sponge moreover is yellow in colour, 
light, elastic, tough and soft—properties which make it 
extremely useful for washing purposes. A closer exami- 
nation of the sponge will show that it is composed of a 
vast number of tiny threads closely interwoven—it is the 
space between these which forms the pores so useful in 
absorbing and retaining water. ‘There are also a number 
of larger openings leading inwards. These, however, 
retain but little water, as can be easily shown by holding 
up a saturated sponge and allowing the liquid to drain 
away—this it does through the large openings. If we 
wish to remove the water from the smaller spaces, we must 
squeeze the sponge. 
