METAZOAN- ORGANIZATION 63 



produced until the last generation of the season, and this time 

 there are both males and females. These mate, the females lay fer- 

 tilized eggs which pass through the winter and hatch as the first 

 generation next spring. These individuals are the stem-mothers for 

 the new season. Some authors speak of this process as ''virgin 

 birth." The honey bee queen can control her offspring to some 

 degree. If her eggs are not fertilized, the offspring are all males 

 (drones). If the eggs are fertilized, as most of them are, only 

 females are produced, these becoming queens if fed abundantly on 

 proper food or workers if fed otherwise. In regard to this state of 

 affairs Lane puts it this way, ''So it comes about, that though a 

 drone bee may become the father of thousands of daughters, he 

 never has a son, nor did he himself have a father.'' 



The eggs of a number of animals, such as frogs, molluscs, worms, 

 sea urchins, and others have been artificially stimulated to continue 

 development by application of chemical, electrical, or mechanical 

 agents. This goes under the name of artificial parthenogenesis. 



Metagenesis is a phenomenon occurring in the life history of a 

 number of scattered species of Metazoa, including the coelenterate, 

 Ohelia; two or three marine worms; and Salpa, the tunicate (a chor- 

 date animal). This process is an alternation of production of sexual 

 individuals in one generation and asexual in the next. The offspring 

 in each case differs from its parents. This is spoken of as alternation 

 of generation. In Ohelia, a coelenterate related to Hydra (to be 

 studied shortly), there is a plantlike, asexual, colonial form, which 

 gives rise to sexual, free-swimming medusae. The medusae produce 

 eggs and sperms which unite in the water and develop into asexual 

 colonies. Metagenesis really involves two methods of reproduction 

 in successive generations of the same species. The significance is 

 somewhat uncertain, but possibly it insures better and more com- 

 plete distribution of individuals than could be secured by only the 

 budding colony. Many of the sexua;lly reproducing plants have a 

 similar alternation of sexual and asexual generations. 



References 



Maximow, Alexander A., and Bloom, William: A Textbook of Histology, Phil- 

 adelphia, 1938, W. B. Saunders Company. 



Hewer, Evelyn E.: Textbook of Histology for Medical Students, St. Louis, 1938, 

 The C. V. Mosby Company. 



