HYDRA AND CCELENTERATES IN GENERAL 133 



Reproduction. Reproduction takes place in Hydra both 

 asexually and sexually; in the former case, by fission and budding, 

 in the latter, by the production of a fertilized egg. 



LONGITUDINAL FISSION. Since the work of Trembley (1744) 

 appeared, a number of zoologists have reported the discovery of 

 double Hydras. These were considered by some as abnormalities, 

 and by others as undergoing the process of longitudinal fission. 

 There seems now to be plenty of evidence to prove that Hydra 

 does reproduce by longitudinal division (112). The distal end 

 of the animal divides first; then the body slowly splits down the 

 center, the halves finally separating when the basal disk is severed 



FIG. 61. Hydra reproducing by longitudinal division. 

 (After Koelitz in Zool. Anz.) 



(Fig. 61). Hydras hsive also been found which bore buds repro- 

 ducing in this manner. This method of multiplication must, 

 however, be rare since it is so seldom seen. Transverse fission has 

 also been reported (m). 



BUDDING (Fig. 54, b). A commoner method of asexual 

 reproduction, and one that is easily observed in the laboratory, is 

 by budding. Superficially the bud appears first as a slight bulge 

 in the body wall. This .pushes out rapidly into a stalk which 

 soon develops a circlet of blunt tentacles about its distal end. 

 The cavities of both stalk and tentacles are at all times directly 



