376 THE BIOLOGY OF HYDRA : 1961 



or chitinous perisarc, develops tentacles at the upper end, hollows 

 out and finally perforates a mouth in the center of the tentacles 

 (see Fig. 1). For 4 or 5 days, this hydra-like animal, growing 

 on a branched stalk, catches Crustacea or other suitable prey with 

 the batteries of nematocysts in its tentacles, ingests them, dissolves 

 their contents which are taken up by a phagocytic process into the 

 endodermal cell layer or transmitted back down along the branching 

 root-like stolon to other individuals in the colony or to the region 

 of apical growth. 



tk \r . «k f r 



D 



V. V V V 



f 



H 



J K 



Fig. 1. Development of Campanularia hydranth. (Taken from time lapse 

 sequence). 



I would like to suggest that these contrasting species of coelenter- 

 ates are useful in studies of the biological basis of senescence be- 

 cause they furnish us with exaggerated models of parallel systems 

 we may observe within more highly evolved metazoa such as human 



