224 THE ZOOLOGIST. 



Harting. They are high, elegantly vase-shaped sponges, which 

 attain a breadth of f and a height of 1^ metres. Mr. Ramsay 

 dredged a massive Ra-phyrus, which weighed several hundred- 

 weight, on the east coast of Australia. 



The colour of sponges is also very variable. Hexactinellid 

 and Calcareous sponges are colourless, and appear brilliantly white, 

 in consequence of the lustre of their spicules. Most other sponges 

 have brilliant colours. Mimicry is rare. Only the forms which 

 possess a sand cortex correspond in colour to the sea-bottom on 

 which they grow. Most Chondrospongim and Cornaciispongice 

 possess glaring colours, presumably for the purpose of warning 

 and frightening other animals. 



The changes of colour exhibited by certain sponges shortly 

 after death are very interesting. Nardo drew attention to this 

 fact in the case of Aplys'ma aerojyhoba as early as 18:33. This 

 sponge is bright sulphur-yellow in the living state, but 

 when exposed to air, or fresh water, it changes this colour to 

 dark blue. 



The body of the higher sponges appears as a mass of mesoder- 

 mal ground-substance, in which cells of various kinds are found. 

 This mass is pervaded by a complicated system of frequently 

 branching canals. All free surfaces are covered with epithelia. 

 The canal system is transgressing, and is essentially different in 

 this respect from the csecal gastrovascular system of higher 

 Coelenterates. On the surface there are numerous small pores 

 which lead into this canal system. 



The entrances to the inhalent canals proper are not to be 

 sought for in the pores of the skin, but lie in the floor of extensive 

 subdermal cavities, into which the inhalent pores lead. Whilst 

 the different parts of the subdermal cavities communicate with 

 each other, the inhalent canals and their branches do not form 

 any anastomoses in the interior of the sponge. They lead into 

 the ciliated chambers, which are spherical or sac-shaped ex- 

 tensions of the canals, clothed with a peculiar epithelium of 

 collared cells. The ciliated chambers possess very small in- 

 halent pores, through which the water passes from the inhalent 

 canal system ; that is to say, the canals are very much con- 

 stricted just before widening to form the ciliated chambers. 

 The inhalent pores are more or less opposite to the exhalent 

 pore, which is much larger and always single. 



