•DIPS INTO MY AQUARIUM. 29 



There is, however, another reproductive process which may be 

 witnessed in the later part of the year. Two distinct kinds of 

 cells are developed within some of the larger globes : the one an 

 egg-sphere {oosphere), and the other a sperm-sphere (anf/ierozoid). 

 In higher plants these correspond to pollen and ovules. The egg- 

 spheres are fertilised by the antherozoids, and a kind of spore is 

 the result. These escape from the decaying parent, and lie 

 dormant till their vitalities are quickened by returning Spring, when 

 they will at once start upon their new career and develop into 

 perfect volvoces, endowed with the powers essential to cell- 

 division. 



(To be continued.) 



The Flapping of a Fly's Wings. — The slow^ flapping of a 

 butterfly's wing produces no sound, but when the movements are 

 rapid a noise is produced which increases in shrillness with the 

 number of vibrations. Thus, the house-fly, which produces the 

 note F, vibrates its wings twenty-one thousand one hundred and 

 twenty times a minute, or three hundred and thirty-five times in a 

 second ; and the bee, which makes the note A, as many as 

 twenty-six thousand four hundred times, or four hundred and 

 forty times in a second. On the contrary a tired bee hums on E, 

 and, therefore, according to theory, vibrates its wings only three 

 hundred and thirty times in a second. Marey, the naturalist, 

 after many attempts, has succeeded, by a delicate mechanism, in 

 confirming these numbers graphically. He fixed a fly so that the 

 tip of the wing just touched a cylinder, which was moved by 

 clock-work. Each stroke of the wing caused a mark, of course 

 very slight but still quite perceptible, and this showed that there 

 were actually three hundred and thirty strokes in a second, 

 agreeing almost exactly with the number of vibrations inferred 

 from the note produced. — Sir John Lubbock. 



