166 REPRESENTATION OF THE 



VII. 



REPRESENTATION OF THE OTHER FORMS OF 

 ALTERNATION IN THE HIGHER ANIMALS, 

 ESPECIALLY IN CONNECTION WITH THE 

 " MATURATION OF SEX. 



1. REASONS have been given in the last Chapter, for drawing 

 a parallel between protomorphic alternation in the lower 

 animals, and a particular feature in the embryogeny of 

 those higher in the scale viz., the implantation of the 

 rudiments of the typical organization on the blastodermic 

 membrane, which after cleavage is formed on the surface of 

 the vitelline mass. On similar grounds of analogy we 

 might look for some representation of the other forms in 

 the period of typical development, and in connection with 

 the evolution of the sexual organs. 



The same analogies, however, would lead us to expect 

 that the traces of such phenomena would be far from evi- 

 dent in the former. Even in the lower animals, as we have 

 seen, gemmation in the orthomorphic stage rarely puts on 

 the form of alternation, because the gemmae seldom sepa- 

 rate as free zooids, generally remaining in adhesion to the 

 common stock, and going along with it and with each other 

 to make up a more or less composite structure. We find 

 further, that, as we ascend to the higher forms, the individu- 

 ality of the associated parts becomes always less marked, 

 the zooids assuming more and more the position of mere 

 organs, and the budding process gradually merging into 

 one of continuous growth. In the higher animals, indeed, 



