120 COMPARATIVE ANATOMY. 



i 



XVI. 



GENERATION. 



GENERATION is the production of offspring. 



Six methods apparent. The first is true generation, 

 the remaining five (agamic) may be considered its acces- 

 sories. 



(1) That of the egg. This, so far as is known, is constant 

 among animals, hence the aphorism " Omne vivum ex ovo." 

 (Harvey.) 



(2) Conjugation. This is the result of union of two or- 

 ganisms apparently without intervention of sexual apparatus, 

 as in Gregarinse. 



(8) Encapsulation. This is the formation of a capsule 

 within the parent tending to engross the area of the entire 

 animal, from the changes within which a new being arises, 

 as in Infusoria. 



(4) Fissuration. This is spontaneous division of parent; 

 each half assuming the shape and properties of the original 

 form, as in Infusoria. 



(5) Gemination. This is the formation of buds (gemmae), 

 which after acquiring the characters of the stock from which 

 they spring, may retain their connection with the parent, as 

 in hydra buds of Eucope, or become detached free gemmae, 

 as in Hydra. Buds may arise beneath the integument the 

 common way or originate from the interior, forming curious 

 ova-like masses, as in Aphis and Cecidomyia. 



(6) Alternate Generation (larval generation, asexual gen- 

 eration, virgin generation, parthenogenesis, polymorphism, 

 metagenesis). When from a freed gemma one or more dis- 

 similar forms arise, and when from these constituting 

 broods of sexless beings other unlike forms issue, either 

 through repetition of the process of gemmation, as in Coryne, 

 or by fissuration, as in Aurelia, and when within these be- 

 ings, in turn, sexual organs are developed, and propagation 



