906 Marvels of the Universe 
A ©“ CHALLENGER” SPONGE. 
The “fronds’’ are bowl-shaped. On the con- 
vex sides are the oscules, on the concave the in- 
current pores. 
affects the corresponding latitudes of Europe. In the 
Southern Hemisphere the Peruvian or Humboldt current 
of the South Pacific, and the Agulhas current of the 
Indian Ocean, the former a cold current, the latter a warm 
one, are best known. The currents of the Indian Ocean 
in general are “wind products,” governed in their 
direction by the prevailing winds, flowing westwards under 
the influence of the north-east monsoon, and eastwards 
when under the influence of the south-western. Thus, 
by these currents flowing in various directions, some 
carrying water hotter than the surrounding sea, some 
carrying cold water and sometimes icebergs, there is pro- 
duced a constant circulation of the waters of the ocean. 
Variations in atmospheric pressure also give rise to 
fluctuations of the level of lake surfaces, to the discharge 
of springs, and modify considerably all tidal phenomena. 
The impulse of the Wind upon a water surface throws the 
latter into pulsations which vary from mere ripples to 
huge billows. The latter often effect much destruction 
upon shores or banks exposed to their action. 
The transport of volcanic dust by Wind may be here 
referred to as another example of the geological work 
done by the atmosphere. After the great eruption of 
Krakatoa, it is estimated that clouds of fine dust were 
hurled from that volcano to a height of seventeen miles ; 
and by the agency of the Wind this material was trans- 
ported for thousands of miles. It is even thought that 
the presence of this matter in the air was the cause of 
the remarkable sunsets witnessed in Europe during the 
autumn and winter of 1883 and the spring of 1884. 
SPONGES 
BY BERNARD C. WHITE. 
Ir would be as well to start this article with two cautions : 
firstly, don’t look upon sponges as plants; and, secondly, 
don’t think that the living creature is at all similar in 
appearance to the prepared sponge of domestic use. 
Sponges are animals, or rather colonies of animals, 
assembled in one indivisible body for their mutual well- 
being. Certainly they are a very low form of animal-life, 
for their methods of reproduction are very plant-like. 
Here is an easy test by which their animal nature can 
be proved: subject a small piece of sponge to the 
flame. It will not burn brightly, but will char, and 
when entirely burnt up, will leave a small charcoal-like 
residue. All the time that it is smouldering it will give 
off a smell very similar to the burning of hazy, a result 
which is seldom to be observed in the burning of 
