36 INANITION AND MALNUTRITION 



Schultz ('06) noted that although the process of asexual budding in Hydra 

 fusca is inhibited by inanition, the differentiation of the testes proceeds, they 

 being among the organs most resistant to starvation. Even in extreme stages 

 the sex-cells (spermatogonia) persist and ripen into spermatozoa (Figs. 7c, 10). 



Whitney ('07), on the basis of very careful and extensive experiments with 

 Hydra viridis, concluded that temperature rather than food supply is the pri- 

 mary factor in sex-production . Low temperature followed by higher temperature 

 causes budding and also formation of sex-organs, irrespective of food conditions. 



Oral area 



Mouth 



Entoderm 



Ectoderm 



root- 



Entoderm^ ^Jf&^Eclbderro 



Fig. 8. — A longitudinal section of Hydra fusca after eight weeks of starvation. Body 

 concontracted; mouth aperture still open. (After Berninger '10.) 



Fig. 9. — A longitudinal section of Hydra fusca after twelve weeks of starvation. Body 

 oval in form; mouth aperture has closed. (After Berninger '10.) 



Hanel ('08) found that neither inanition nor low temperature causes sex- 

 production in Hydra grisea. Krapfenbauer ('08) obtained positive results by 

 lowered temperature, but not by inanition. Frischholz ('09) found that within 

 certain limits of temperature, sex-production in Hydra tends to appear in definite 

 cycles of 20 to 40 days, depending upon the nutritional conditions. Even in 

 extended inanition, however, sexual forms appear, either male or female (the 

 strains used being always monosexual, never hermaphroditic). A change of 

 temperature is unnecessary, but may accelerate sex-production. However, 

 permanent exposure to high temperatures in Hydra grisea or to low tempera- 

 tures in Hydra fusca, permanently inhibits sex-production, irrespective of the 

 degree of nutrition. Finally, Berninger ('10) again found that in Hydra fusca 

 (also in Dendrocoelum lacteum) inanition stimulates the development of the 

 testes, with abundant ripening of the spermatozoa during starvation. 



In summary, it is evident that Hertwig was correct in concluding that 

 sexual differentiation in Hydra is a complicated phenomenon, various factors 

 being involved. Besides temperature and nutrition, there is probably a cyclic 

 or seasonal variation, and other hereditary characteristics, apparently varying 

 in different species or strains of Hydra. 



