Embryology. II! 
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 
Fic. 28.—//ydra viridis, 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 amulticellular Metazoén,—this great principle 
of co-organization is but dimly nascent in the cell- 
