CHAPTER VIII 

 BRITISH SPONGES 



IT seems to be the popular opinion that sponges are essentially 

 natives of the warmer seas, and it will probably be a surprise 

 to many young amateur naturalists to learn that there are about 

 three hundred species of this sub-kingdom of the animal world to be 

 found on our own shores. It must not be thought, however, that 

 they are all comparable with the well-known toilet sponges in 

 regard to either size or general form and structure, for some of 

 them are very small objects, no larger than about one-twentieth of 

 an inch in diameter, and some form mere incrustations of various 

 dimensions on the surfaces of rocks and weeds, often of such 

 general appearance that they would hardly be regarded as animal 

 structures by those who have not studied the peculiarities of the 

 group. 



Sponges are known collectively as the Porifera or Polystomata, 

 and constitute a separate sub-kingdom of animals of such distinct 

 features that they are not readily confused with the creatures of 

 any other group. Their principal characteristic is expressed by 

 both the group names just given, the former of which signifies 

 ' hole-bearing,' and the latter ' many openings ' ; for in all the 

 members of the sub-kingdom there are a number of holes or pores 

 providing a means of communication between the body cavity or 

 cavities and the surrounding water. Most of these holes are very 

 small, but there is always at least one opening of a larger size at 

 the anterior end. 



It will be seen from what we have just stated that sponges 

 exhibit a distinctly higher organisation than the protozoa described 

 in the last qhapter, inasmuch as they possess a permanent body- 

 cavity that communicates with the exterior ; but in addition to 

 this there are many points of differentiation of structure that 

 denote a superior position in the scale of life. 



