22 NATURAL HISTORY OF OUR SHORES 



needle-shaped spicules. This collar is under control, the 

 sponge having the power of expanding and closing it. This 

 sponge is the one shown in Fig. 5. 



Closely allied to it, and still more abundant, is a flattened 

 leaf-like form, Grantia compiessa (Fig. 6). Structurally this 

 is much the same, but the spicules do not project beyond the 

 surface, and there is no collar. The large cavity within 

 (when it is submerged and bulges out a little) is often made 

 use of as a shelter for various little crustaceans. One 

 curious little isopod, which will be described in due course, 

 Anceus maxillaris, sometimes fairly crowds the cavity. 



These two sponges belong to the Calcispongia. 



Other forms of Calcispongia are found in the same 

 localities one of these, Leucosolenia botryoides, forms 

 twisted masses, looking like a tangle of rather abraded 

 white crochet cotton, the oscular projecting at intervals. 



We will take one of these calcisponges as a type for an 

 elementary survey of sponge anatomy, but must first 

 digress a little for an explanation of the term " cell." 



Whether or not this term is aptly chosen, it is used by 

 biologists to designate the smallest masses of matter which, 

 singly or collectively, evince that series of phenomena 

 which we term " life." 



These cells are minute, some less than a thousandth of 

 an inch in diameter, others just visible to the unaided eye. 



They vary in form: some are round, others oval, flattened, 

 star-shaped, etc., according to the tissues which they 

 constitute. 



They multiply by division i.e. when one has attained 

 a certain size it divides into two, and so on and it is by 

 this multiplication of its constituent cells that the growth of 

 an organism, let it be a sponge or a mammal, is effected. 



In the vegetable kingdom each cell is usually enclosed 

 by a bounding membrane of a substance rather different 

 to its contents, termed cellulose. In the animal kingdom 



