small, hollow tentacles. When at rest 

 the hydra contracts until it is a short, 

 globular body, the tentacles being short, 

 blunt and club-shaped, but when the ani- 

 mal is active and expanded the body is 

 long and cylindrical, and the tentacles 

 are long, narrow and constantly twist- 

 ing" about. Should an insect or other 

 minute animal chance to stray his way 

 when the hydra is active, it is quickly 

 paralyzed by the lasso barbs or nettling 

 organs and then drawn into the mouth 

 by the tentacles. The hydra is not sta- 

 tionary, but is able to move from place 

 to place by gliding along, being aided 

 in this operation by a sticky fluid which 

 is secreted by cells of the pedicel. 



Like many others of the lower ani- 

 mals, the hydra is capable of wonder- 

 fully reproducing lost parts. For ex- 

 ample, if a hydra be cut in two, each 

 piece will develop into a perfect animal, 

 and if it be sliced into thin rings or 

 cut in longitudinal sections each piece 

 will grow and form a perfect hydra. 

 Specimens have been even turned inside 

 out, and in a short time the animal ho? 

 been able to digest food in a stomach 

 made of the outside of the body. So 

 well marked is this reproductive func- 

 tion that it is almost impossible to kill 

 a hydra witli a knife. 



The Hydroids perpetuate their species 

 in four different ways ; first, by budding, 

 in which a new Hydroid simply grows 

 out from the older animal; second, by 

 fission or a splitting up of the animal, 

 as in hydra ; third, by the formation of 

 medusa; or jelly fishes ; and fourth, by 

 means of true eggs. The life history of 

 a common Hydroid may be summarized 

 as follows : the Hydroid develops a 

 bud-like organ called a reproductive 

 calycle, which produces small young 

 called medusae or jelly-fishes. These in 

 turn produce eggs from which little 

 swimming embryos develop. These 

 finally fall to the bottom of the sea and 

 grow into perfect Hydroids. It will 

 thus be seen that the young Hydroid is 

 never like its parent, but like its grand 

 parent, the Hydroid producing jelly- 

 fishes, and the jelly-fishes Hydroids. 

 This is called by scientists the alterna- 

 tion of generations. 



It will be seen by the above account 

 that the species of this class of animals 



are dimorphic or have two forms. This 

 is a very interesting fact and one that 

 can be duplicated in but few branches 

 of zoology. The Medusa or jelly-fish is 

 very beautiful and of such a size as 

 to be readily seen and examined. It 

 consists of a bell or umbrella-shaped 

 structure to which is suspended, in 

 the center, a hollow stomach, and 

 from this organ four canals radiate 

 which open into a circular canal sur- 

 rounding the edge of the bell-shaped 

 structure. From the edge of this disk 

 several thread-like tentacles hang down 

 which contain lasso cells and have the 

 same power of stinging or paralyzing 

 their prey as do the coral polyps. In the 

 Physalia, or Portuguese Man-of-War, 

 these tentacles are often many feet in 

 length. The animal has been known to 

 cause the death of swimmers who have 

 ventured into deep water, and have been 

 benumbed by the multitude of darts 

 thrown out by the tentacles. The Me- 

 dusae possess a well-marked ring of 

 nerve matter surrounding the edge of 

 the bell and they also have eyes and 

 simple ears situated at various places 

 on the edge of this disk. 



During their development the jelly- 

 fishes pass through fully as wonderful 

 changes as do the butterflies from a 

 caterpillar to the perfect insect ; in fact, 

 they pass through a metamorphosis. 

 The Aurelia, a common New England 

 jelly-fish, lays its eggs in the late sum- 

 mer. A month or so later these eggs 

 have developed into a hydra-like animal 

 called a scyphistoma, in which stage it 

 remains for about eighteen months. At 

 the end of this time the hydra develops 

 a number of cup-like disks, tentacles 

 bud out, and the animal assumes the 

 strobila stage. One of these disks be- 

 comes detached, swims away and finally 

 develops into the fully formed Aurelia, 

 just two years after it was deposited as 

 an eg^ from the adult Aurelia. This 

 is so like the metamorphosis of the but- 

 terfly that we can almost match the 

 changes stage for stage. 



Few objects of the sea shore are as 

 beautiful or as interesting as the jelly- 

 fishes. If the seaside visitor takes a 

 boat and rows upon a bay or the ocean, 

 either by day or by night, he is sure to 

 see one or more of these delicate, jelly- 



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