318 



THE BIOLOGY OF HYDRA : 1961 



Fig. 1. High-speed photograph of a swimming medusa. Magnification 

 approximately 3X. 



4) a basal region by which it attaches to the substrate and/or 

 to neighboring hydranths. 



These hydranths carry on asexual reproduction by producing 

 three types of buds ( Fig. 3 ) : 1 ) hydranth buds which remain 

 attached to the parent to form small colonies; 2) frustule or planu- 

 loid buds which separate from the parent and creep a short dis- 

 tance before developing into new polyps; and 3) medusoid buds 

 which are released as free-swimming medusae. Under optimal 

 conditions all three types of buds are formed laterally as outgrowths 

 of the body wall near the middle or budding region of the hy- 

 dranth {vide ref. 21). Differential growth in the case of hydranth 

 buds results in the subsequent basal attachment of adjacent hy- 

 dranths. 



Several previous workers have observed the budding processes 

 of Craspedacusta polyps (3, 6-10, 12, 14-22), but only Reisinger 

 (20, 21) and McClary (14) have studied specific factors which 

 influence the production of buds under laboratory conditions. 

 Reisinger (20, 21) found that a sudden elevation of tempera- 

 ture from 20" to 25-27° could initiate medusa budding. Mc- 

 Clary (14) studied the growth and reproduction of polyps at 



