The Hydra. 



W. A I'OYSER, Hammond, Indiana. 



T N his aquaria or tanks the fish 

 -*- breeder may find, attached by its 

 base to the stems of aquatic plants, a 

 very small animal, just large enough to 

 be seen without the aid of a glass, of a 

 pale green or brown color. This is the 

 common hydra, technically Hydra viridis 

 (green hydra) or Hydra fiisca (brown 

 hydra). It possesses a gelatinous, sub- 

 cylindrical body which may undergo 

 various changes of form. One end 

 expands into a foot or disk by which 

 the creature attaches itself, or moves 

 slowly along as its own volition dictates: 

 while a mouth surrounded with five or 

 more tentacles is at the opposite end. 

 These tentacles or feelers are exceedingly 

 contractile: one moment they may be 

 long, slender threads, at the next, or 

 after a meal, blunt knobs. 



The most remarkable, as well as the 

 most interesting characteristic of the 

 hydra is its power to overcome animals 

 more active and muscularly stronger 

 than itself. The surface layer of the 

 body and feelers contain numerous 

 nematocysts, popularly termed lasso- 

 cells or nettling organs, about one two- 

 hundredth of an inch in diameter. Each 

 sac-like or bag-like cell is filled with a 

 poisonous fluid, and coiled vip in the 

 fluid is a long thin filament in a state of 

 tension. Groping about with its flexible 

 arms, the hydra touches an animal 

 swimming near it, the contact rupturing 

 the cell, when both fluid and filament 

 are forcibly ejected, the end of the fila- 

 ment entering the victim, and piercing 

 it ready for the poison. While the 

 hydras are not powerful enough to in- 

 commode the larger animals, Daphnia, 

 Cyclops and newly hatched fish are 

 readily overcome. This is well known 

 to fish culturists who use every means 

 to rid the tank of the pests. 



The prey when mastered, is thrust by 



the tentacles into the body cavity. On 

 the inside are simple ciliated amoeboid 

 cells into which particles of the food 

 pass to be digested. The animal posseses 

 no real stomach or intestine, the inside 

 of the body-sack being practically a 

 colony of amoebae which serve the same 

 purposes. 



The hydra propagate mostly by gem- 

 mation or budding. Throughout the 

 summer, buds are produced trom the 

 side of the animal, which increase in 

 size, become open at the free end and 

 gradually acquire feelers. The pedicel 

 becomes thinner by degrees, and finally 

 the young polp frees itself from the 

 parent and begins an independent 

 existence. As in other animals, the 

 hydra also reproduces sexually from an 

 egg, but the sexes are not separate. 

 Budding, which is but a process of 

 natural self-division, is carried on to a 

 large extent, more individuals being 

 produced in this way than from eggs. 

 In autumn an egg is produced at the 

 base of the body-sack, and these probably 

 sexual eggs or resting bodies lie dormant 

 until the next spring, when they are 

 hatched, and a new generation produced. 

 Like some other lower animals, the 

 hydra may be multiplied by mechanical 

 division. Cut an animal in two, or, 

 slice into a number of rings, and each 

 will eventually grow a crown of tentacles 

 and become a perfect specimen. It was 

 once claimed one could be turned in- 

 side out, and the former outside cells 

 would perform the digestive functions^ 

 but this is now believed to be in error. 



"Every good man has his Hobby, and 

 every haid- working man should have 

 one." Athenaeum. 



In the woods, a man casts off" his years, 

 as the snake his slough, and at what 

 period soever of life is always a child. 



Emerson. 



