PROTECTIVE RESEMBLANCE 



13 



described as belonging to them. It is evident that the sponge 

 possesses irritability and contractility. It has the instincts of 

 self-preservation and of the perpetuation of its species. No one 

 can correctly interpret the psychologic phenomena of any 

 animal until he has passed through the same psychic phenomena 

 as that animal, and then become a man with the memory of 

 these experiences and what they signified to that animal. Since 

 we cannot do that, we must be content to infer the significance 

 of certain biologic phenomena from comparison with our own 

 experiences. 



Environment. As has been said, sponges are greatly in- 

 fluenced as to their shape by the objects to which they are at- 



Fig. 6. A young sponge. (After Burnet.) 



tached and by the depth and currents of the water. They are 

 much more nearly uniform in deeper waters. The plastic 

 sponge well illustrates the influence of gravity (geotropism) 

 upon an animal. It also shows rheotropism. 1 



Protective Resemblance. Their protective resemblance is 

 exceedingly good. They look so much like the seaweed and 

 other aquatic vegetation that they are well concealed from 

 the animals which prey upon them, such as worms, crustaceans, 

 mollusks, and other marine invertebrates. Their tough, horny 

 texture and their silicious or calcareous spicules are also a 

 means of protection. Their characteristic odor, said to re- 

 semble garlic, makes them distasteful to fishes. 



1 See Glossary. 



