STRUCTURE OF TYPICAL HY1JROID. 37 



EXPLANATION OF FIG. 4. 



The Structure of a typical Hydroid 

 (Hydra), and the distinctive difference 

 between Budding and Ova production ; also 

 a dart cell. 



(From Parker and Haswett, after Schneider). 



A. 





m. 



Mouth. 



end. 



Endoderm cell with pseudopodium. 



end' 



Endoderm cell with flagella. 



msgl. 



Mesoglsea, intermediate membrane. 



ect. 



Ectoderm 



dt. 



Large dart cells. 



dV 



Small dart cells. 



bd. 



Bud. 



on. 



Ovum. 



sp. 



Spermarium. 



B. 





tr. 



" Trigger-hair." 



dt. s. 



Dart sack. 



thd. 



Thread coiled within the sack. 



dt. c. 



Dart cell. 



nu. 



Nucleus. 



