THE BIOLOaY OF THE ANIMAL 



Sponges 

 Example 1. — Skeleton of Toilet Sponge (Empongia Sp.) 



Material. — Specimens may be obtained at any drug 

 store. It must be borne in mind that these are almost 

 invariably imperfect, since in preparing the sponge for 

 market it is trimmed more or less to give it a symmet- 

 rical shape. The trimming is usually confined to the 

 base, which contains a collection of debris consisting of 

 sand, small pebbles, pieces of shells, etc., whose presence 

 would affect the market value of the sponge. Branched 

 forms also are clipped to make them into a more conven- 

 ient shape. Students will readity detect the places which 

 have been trimmed by the fact that the surfaces are 

 smooth and even. The small sponges used for washing 

 slates are generally pieces sheared off larger sponges. 

 It is well to have for comparison some fine surgeon's 

 sponges as weU as the coarser kinds used for washing 

 carriages. 



Besides the specimens the student will need a mag- 

 nifying -glass, compound microscope, scissors or sharp 

 knife, and a tumbler of water. 



Method of JExamination. — The sponge skeleton should 

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