SPONGES 



Associates. — Fresh water sponges harbor very inconspicuous 

 little parasites — the six-legged larvae of Spongilla-flies which 

 descend into the osteoles or pierce their way into the soft 

 sponge cells with their sharp mouth-parts (Fig. 187). They 

 can not only pierce the cells, but they can suck out the con- 

 tents as conveniently as we can drink through a straw. Each 

 of their slender mandibles is hollowed out on its inner side, 

 and when held closely together they make a perfect tube 

 through which the watery content of the sponge cells is easily 

 drawn. Spongilla-flies have transparent bodies and their 

 stomachs are always so full of sponge that they are literally 

 sponge-colored, inside and out, and a more convincing camou- 

 flage would be hard to find. One must search for one of these 

 larvae with a lens ; it will scarcely be noticed unless it is moving 

 and even then it \odks like a piece of sponge on legs. 



Study and collecting. — It is difficult to distinguish fresh 

 water sponges and in order to identify a species one should 

 know the form of the colony, the spicules and gemmules as 

 well. When specimens are collected for identification, care- 

 ful note should be made of the living colony and its habitat 

 and a piece of it scraped off and preserved in alcohol or forma- 

 lin. Gemmules can be found in late autumn, occasionally in 

 summer, and their general structure can be made out with a 

 pocket-lens, but a microscope is necessary to see the spicules. 



A winter study of living sponges. — An interesting winter 

 study of gemmules can be made with only a dish, some pieces 

 of glass, and a pocket-lens for tools. In early winter, gemmules 

 look like so many fig-seeds clustered among the spicules (Fig. 

 84) and may easily be scraped into water and taken home. 

 Then water, preferably from their own brook or pond, should 

 be poured into a deep pie-plate, a few pieces of clean glass 

 placed in the bottom, the dish set where it will not be jarred, 

 and finally the gemmules dropped onto the glass. They 

 should be left undisturbed for two or three days, at room 

 temperature and out of direct sunlight. A little fresh water 



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