Embryology. 



in 



said that some of the higher Protozoa foreshadow this 

 state of matters in forming cell-colonies, it must now 

 be noted that the cells composing such colonies are 

 all of the same kind ; and, therefore, that the principle 



FIG. 28. Hydra mridis, partly in section. M, mouth ; O, ovary, or 

 bud containing female reproductive cells ; T, testis, or bud containing 

 male reproductive cells. In addition to these buds containing ger- 

 minal elements alone, there is another which illustrates the process of 

 "gemmation" i. e. the direct out-growth of a fully formed offspring. 



of producing different kinds of cells which, by mutual 

 co-adaptation of functions, shall be capable of con- 

 structing a multicellular Metazoon, this great principle 

 of co- organization is but dimly nascent in the cell- 



