DEVELOPMENT OF HYDRA. 12? 



of life are, they are as admirably adjusted one group 

 to the other, as the higher animals are to feed 

 on and keep down the higher plants. Moreover 



Fig. 87. Fig. 88. 



First stage of development of Second stage of development 

 Hydra. of Hydra. 



there is the same kind of dependence on each other's 

 needs. The microscopic plants, such as desmids and 

 diatoms, give out just the oxygen which amcebas, 

 hydras, or rotifers require. Again, we find amongst 

 the lower types of animal life the same broad 

 differentiations which stand out so visibly among 

 the higher, of carnivorous and herbivorous. Death 

 is as much the law of the life of the microscopically 

 small as it is of such creatures as the tiger and 

 the antelope. 



The rotiferal animalcules may be obtained and 

 kept in any abundance. Some of them, as for instance 

 the Melicerta, will be found attached to the various 

 small leaves of plants. These are usually deno- 

 minated " stalked " rotifers. All around it the Meli- 

 certa builds up a caddis-worm-like case, composed 

 of pellets of rejected or excreted food. With 



