402 THE MICROSCOPE. 



sponge there is usually a brownish orange-coloured mem- 

 brane, which Schultze found presented the marked cha- 

 racters of a minute parasitic polyp, probably alcyonarian, 

 which inhabited the oscula and their passages during the 

 life of the sponge. 



" The glassy wisp of Hyalonema is certainly very re- 

 markable, but it is not entirely without analogy. Hyalo- 

 nema seems to represent the extreme form of a little group 

 of sponges, including, with probably a few other forms, 

 Euplectella (A Icyonellum) speciosa (Quoi and Gaiinard), and 

 E. cucumer (Owen). The last-named is an oval sponge 

 with siliceous spicules, in form and character somewhat 

 like the spicules of Hyalonema. From one end of the 

 sponge a tuft of long siliceous threads, resembling in 

 structure those of the Japan sponge, twine round a stone 

 or other foreign body. Dr. Bowerbank isolated one of 

 the spines of Euplectella, three inches long." See Intel- 

 lectual Observer, March, 1867. 



INFUSORIA. 



The term Infusoria is applied to a certain class of 

 animals because they were first discovered in water whera 

 vegetable matter was decomposing, the infusion was con- 

 sidered necessary for their production. Now, however, it 

 rs an established fact, that they are in a healthier state of 

 existence when taken from pure streams and clear ponds 

 than from putrid and stagnant waters. A little bundle of 

 hay, or sage leaves, left for about ten days in a mug con- 

 taining some pure rain-water, caught before entering a 

 butt, produces the common wheel-animalcules, which are 

 found adhering to the sides of the mug near to the surface 

 of the water. The only use of the vegetable matter seems 

 to be to facilitate in some way the development of the ova 

 of animalcules which find their way into the water. It 

 was at one time thought an indispensable condition that 

 air be admitted to the infusion : but even this element is 

 not absolutely needed in the case of infusorial life ; and 

 the appearance of living organisms at all under the circum- 

 stances, has been regarded as important evidence in favour 

 of the doctrine of spontaneous generation. 



