HYDRA FUSCA 151 



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which are like the original in shape but much smaller in size. 



Some of the experiments described were originally performed 

 long ago, by Trembley in 1740 ; but they have since been 

 confirmed by other investigators. 



Sexual Reproduction. By the method of budding Hydra 

 may multiply indefinitely as long as it has plenty of food. It 

 has also a second method of reproduction by a true sexual proc- 

 ess. Under certain, not well-understood, conditions the animal 

 produces outgrowths on its side, shown in Figure 69 C, which 

 are the sexual glands, ovaries, o, and spermaries, s. Within 

 them are produced special cells, called eggs and sperms, which 

 unite with each other in a manner similar to that seen in the 

 cells of Pandorina (page 74). The significance of this repro- 

 duction will be noticed in a later chapter. 



Hydra, as will be seen from the above description, possesses 

 the systems of alimentation, metabolism, motion, and reproduc- 

 tion. Circulation is wanting; respiration is carried on through 

 the general surface of the cells; no excretory system is found, each 

 cell probably excreting its waste products directly into the 

 water; support is unnecessary in such a small animal; the rudi- 

 ments of nerves suggest the beginning of a coordinating system. 



THE RELATION OF THE WHOLE ORGANISM TO ITS DIFFER- 

 ENT PARTS 



With the appearance of multicellular organisms we also find 

 that the entire animal has now a life more or less independent 

 of the life of its parts. The multicellular animal or plant lives 

 a life as a complex, and in addition each cell has a life of its own; 

 so that we can distinguish, in a multicellular animal, a life of 

 the organism as a whole and a life of its separate cells. It is 

 possible for the death of the organism as a complex to occur 

 while the individual cells still remain alive. It is true that in the 

 multicellular organism each of the individual cells is dependent 

 upon the activity of the whole to keep it properly nourished and 

 supplied with the necessary conditions of its life. The different 



