64 POPULAR ILLUSTRATIONS OF 



What, then, is a Sponge ? " What I use in my bath every 

 morning," answered an impertinent person who was looking over 

 my shoulder when I was writing the question. 



But this self-evident answer, like many other utterances, is only 

 half true, for a Sponge is a great deal more than that when alive. 

 Place the Sponge on the table before you and you will notice that it 

 is covered with openings of various sizes, all leading to passages 

 in the interior. Now, these passages, which tunnel the whole 

 structure, are lined, when the Sponge is alive, with a more or less 

 extensive layer of sarcode, which, as I have already explained, is the 

 protoplasm which constitutes the bodies of all Protozoa, whether 

 Gregarinid, Infusoria, Rhizopod, Eadiolaria, or Sponge. 



Now take your dead Sponge into your hand, and place it in water, 

 and if you watch it carefully you will see the water enter in at the 

 smaller pores till the Sponge is full. Now squeeze it, and you will 

 notice that the water runs out of the larger openings, and, that 

 when you have squeezed out all the water, the Sponge will suddenly 

 dilate to its full size, showing that it possesses the power of con- 

 tractility. 



But the Sponge, when tenanted by its layer of sarcode, can do all 

 that you have done with your hands. It can contract its skeleton, 

 and force out the water from the large or efferent openings, just as 

 you did when you squeezed it, and it can then relax the texture, 

 allowing the fluid containing its food to enter in by the small or 

 afferent openings. 



A now venerable grey-headed philosopher, who has for forty years 

 been silently working at University College (the well-known and 

 respected Dr. Grant), was the first person who saw the living Sponge 

 do what I have described ; and well indeed can I share the delight 

 which he must have felt when he first saw the magnificent sight. 

 A lump of jelly contracting its skeleton as perfectly as the muscular 

 finger of the highly-organised man ! And small fountains of water 

 pouring out of the large openings, containing, among effete and 

 digested matter, ova, or eggs, or germs of future Sponges ! Let us 

 have his own description. It has been often quoted, but not once 

 too often : 



" On moving the watch glass, so as to bring one of the apertures 

 on the side of the Sponge fully into view, I beheld, for the first 

 time, the splendid spectacle of this living fountain vomiting forth, 

 from a circular cavity, an impetuous torrent of liquid matter, and 

 hurling along in rapid succession opaque masses, which it strewed 

 everywhere around. The beauty and novelty of such a scene in the 

 animal kingdom long arrested my attention ; but, after twenty-five 

 minutes of constant observation, I was obliged to withdraw my eye 



