294 The Mickoscope. 



HINTS ON THE FRESHWATER SPONGES. 



BY HENEY MILLS. 



\ S the time is near at hand when the freshw'ater sponges may be 

 -*■ ^ found in places where they grow sufficiently mature for 

 classification, a few hints on their appearance and on collecting and 

 mounting them may be acceptable to many readers of The Microscope. 

 It should be understood that what we find for sale in shops as 

 sponge is merely the fibrous skeleton of a few species of marine 

 sponge, which have been changed from their natural appearance by 

 processes of cleansing and bleaching. These sponges have no spicula, 

 but are tough and of a silky softness after being used a little. The 

 freshwater sponge, on the contrary, is entirely destitute of fiber, the 

 skeleton consisting of a framework of siliceous spicula, that is, little 

 double-pointed needles of silex. These are held together and in 

 position by the sarcode or fleshy mass of the sponge. This fleshy 

 mass is a dense, somewhat jelly-like substance, which, on being dried, 

 frequently shrinks away leaving to the unassisted eye little to be 

 seen but the skeleton that supported it while living. In this condi- ■> 

 tion the specimen might be mistaken for the ordinary commercial 

 sponge, but, unlike it, may be reduced to an almost impalpable 

 powder by rubbing between the thumb and finger. 



The vital organs of the sponge consist of flagellate animalculse 

 placed in large numbers around little chambers called ampullaceous 

 sacs. These animalcule, by the united and continuous action of 

 their flagella, produce a stream of water through the chamber. 

 Several of these small streams unite in a larger one and these again 

 unite to pass the water and effete matter out of the sponge through 

 the largest openings, each of which is called a cloaca. The water 

 for the supply of these small streams enters through innumerable 

 pores at the base of the sponge, which suggest the name porifiroi for 

 the whole family of sponges. The motion of the water, in both its 

 ingress and egress may be seen in young and healthy specimens held 

 in a watch-glass under the microscope, or even with a good pocket 

 lens when the specimen is held in a thin glass tumbler. Small 

 specimens may be preserved for weeks in a jar or tumbler containing 

 some aquatic plants, such as the Lemna or Utricularia. One inter- 

 esting feature in these young and growing sponges will well reward 

 the student even if obsei-ved after some failures and disappointment 

 in watching for it. It is the formation of a more or loss elongated 

 transparent tube or "chimney" on the surface of the sponge. It 



