STRUCTURE OF TYPICAL HYDROID. 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 Haswell^ after Schneider}. 



A. 



m. Mouth. 



end. Endoderm cell with pseudopodium. 



end 9 Endoderm cell with flagella. 



msgl. Mesoglsea, intermediate membrane. 



eat. Ectoderm 



dt. Large dart cells. 



dt' Small dart cells. 



bd. Bud. 



or). Ovum. 



sp. Spermarium. 



B. 



tr. l ' Trigger-hair. " 



dt. s. Dart sack. 



thd. Thread coiled within the sack. 



dt. c. Dart cell. 



nu. Nucleus. 



