416 E. R. Downie, 
Table of contents. 
Historical resumé, male organs of Hydra 
Species of Hydra ; } 
viridis, grisea, fusca, dioecia. 
IT, en nomen novum 
The spermaries: location 
Location in dioecia 
Time of appearance 
Form À 
Maturation and Dre 
Size and structure 
Early stages of formation 
Relation of sexual reproduction to budding aad to een 
Possible causes of sexual reproduction tested experimentally 
Change of temperature 
Change of osmotic pressure . 
Change of ion concentration 
Change of food conditions 
Resultsn (as ST ALI 
Material 
Methods: 
Fixation 
Staining 
Sections 
Mounting . . . 
The tissues of Hydra: 
Ectoderm and endoderm . 
Interstitial cells . 
Structure . 
Derivation 
Migration . 
The cell generations in men: al by measure- 
ments 
395 
