168 
POPULAR SCIENCE REVIEW. 
is commonly meant by spongy, and the material having been 
likened to horny substances, has received the name of keratose 
from the Greek kevas , a horn. The term is so thoroughly ac- 
cepted, that it would be impracticable to change it, although 
the material somewhat differs chemically and physically from 
horn. It has, however, the characteristics of an animal sub- 
stance, and contains sixteen per cent, of nitrogen. 
If, after noticing the characters of common sponge — its larger 
and smaller pores, its tendency to assume regular forms, cup- 
shaped, flattened, &c. — and the evidence presented by its base of 
having been fixed or rooted to a rock, the eye is turned to that 
exquisite and now not uncommon object, Venus’ Flowerbasket 
(. Euplectella speciosa ), quite a different material meets the view. 
The elegant horn-of-plenty-shaped object is seen to be composed 
of glassy fibres crossing, and apparently woven together like 
skilled basket-work, from whence its scientific name, Euplectella , 
well plaited or woven, was obviously suggested. lake the 
common sponge, this shows that it was rooted by a basal 
end, and it exhibits a similar variety of larger and smaller 
pores. The common sponge may be taken as the representative 
of the keratose group, the Euplectella of the siliceous or flinty 
group, for the glassy threads of which it is composed are de- 
posits of silex from living threads of animal matter. 
A third group of sponges have calcareous or carbonate of 
lime skeletons, and both these and the siliceous ones are re- 
markable for the presence of spiculse of various shapes. In 
Bowerbank’s “ British Spongidse,” the most accessible work on 
the subject, the three orders are ranged thus : Calcarea, Silicea, 
and Keratosa, and a subdivision of the latter is described as 
having u spiculated Keratose fibre.” It is, however, from the 
two former groups that the curious and beautiful spicuke so com- 
monly found in microscopical cabinets are derived ; the ordinary 
shapes of which are well known to many who have never paid 
attention to the organisms from which they are derived. 
A good conception of the more obvious sponge characters 
may be derived from a passage in Dr. Bowerbank’s book. He 
says : “ Whatever may be their form, or however they may differ 
from each other in appearance, there are certain points in their 
organisation in which they all agree. In the first place, how- 
ever variable in its form and mode of structure, there is al- 
ways a skeleton present, in which the rest of the organic parts 
are based and maintained. Amidst this skeleton, and inti- 
mately incorporated with it, are the interstitial canals, usually 
of two series : the first appropriated to the incurrent streams of 
the surrounding water, and the second to the excurrent streams, 
which they conduct from the interior of the sponge to the 
oscula at its surface, through which they are discharged.” 
