xxi REPRODUCTION 231 



A, bd-}. These enlarge and take on the characters of ten- 

 tacles : a mouth is formed at the distal end of the bud, 

 which thus acquires the character of a small Hydra (Fig. 

 49, A, bd^]. Finally the bud becomes constricted at its base, 

 separates from the parent, and begins an independent ex- 

 istence. Sometimes, however, several buds are produced at 

 one time, and each of these buds again before becoming 

 detached : in this way temporary colonies are formed. But 

 the buds always separate sooner or later, although they 

 frequently begin to feed while still attached. 



It is a curious circumstance that Hydra can also be mul- 

 tiplied by artificial division : the experiment has been tried 

 of cutting the living animal into pieces, each of which was 

 found to grow into a perfect individual. 



As in Vaucheria and Nitella, the sexual organs or gonads 

 are of two kinds, spermaries and ovaries. Both are found 

 in the same individual, Hydra being, like the plants just 

 mentioned, hermaphrodite or mon&cious. 



The spermaries (Fig. 49, B, and Fig. 50, A, spy) are white 

 conical elevations situated near the distal end of the body : 

 as a rule not more than one or two are present at the same 

 time, but there may be as many as twenty. They are per- 

 fectly colourless, even in the green and brown species, being 

 obviously formed of ectoderm alone. 



In the immature condition the spermary consists of a little 

 heap of interstitial cells covered by an investment of some- 

 what flattened cells formed by a modification of the ordinary 

 large cells of the ectoderm. When mature each of the small 

 internal cells becomes converted into a sperm (Fig. 50, G), 

 consisting of a small ovoid head formed from the nucleus of 

 the cell, and of a long vibratile tail formed from its proto- 

 plasm. By the rupture of the investing cells or wall of the 



