THE SIMPLEST ANIMALS 1 5 



has been added a little carmine soon reveals the fact that 

 it is not, as at first appears, a vegetable growth, incapable 

 of independent action, since the coloured water can be seen 

 to be flowing in a rhythmic pulsating manner. The 

 holes or pores of the sponge lead to a complex series of 

 canals off which branch small chambers lined with hairlike 

 whips which ceaselessly lash the water, and by so doing 

 set up currents that carry food to the sponge's interior. 

 The non-assimilated matter is ejected by outflowing 

 currents which escape by special openings. The body 

 substance as seen in the bathsponge is composed of minute 

 pieces of a material chemically allied to silk, and these 

 in life are bound together by a slimey pulpy tegument 

 often of vivid coloration. Sponges are reproduced by 

 means of egg-cells. The larvse hatched from these lead 

 free-swimming lives for a few days, later settling down and 

 forming the basis of a sponge colony which by cellular 

 division may eventually increase to giant proportion. 



Sponges are classified according to the presence or 

 absence of a skeleton and its nature. The pretty little 

 Flask Sponges (Sycon), which build their skeletons of car- 

 bonate of lime, are abundant amongst tufts of seaweed. 

 They vary from a half to seven inches in length, and if 

 placed in water will demonstrate the circulatory system 

 common to the entire order. 



The graceful Fig Sponge (Ficulina) seems to be especially 

 associated with a hermit crab. Other sponges of this 

 order become attached to the shells of crabs or encrust 

 the mollusc homes affected by hermit crabs, on which they 

 may grow to a large size. When this occurs the sponge 

 may almost completely cover the shell, leaving the 



