26 



growth of the cells at thepoint where the tentacles arise, 

 and the out-pushing of the tissue in the process seems to 

 affect the tissue over a considerable area, so that diver- 

 ticula of the coelenteron and of the mouth extend in the 

 direction of each of the tentacles, A stellate form re- 

 sults, the mouth being in the shape of ^. cross. This cor- 

 responds exactly to the condition in the medusa, especially 

 in young specimens (Fig, 2G ) in which the twisting which 

 obsc^ires the true relation of parts has not yet taken place* 

 In a three-or f ive-tentacled hydra the number and arrange- 

 ment of the oral lobes corresponds with the number and ar- 

 rangement of the tentacles. Figure 12 represents a polyp 

 with five radial parts, in which one lobe of the mouth is 

 bifurcated. This condition is very similar to that fre- 

 quently met with in the adult medusae. Hargitt figures a 

 specimen in his "Variations among Hydromedusae" (1901, PI. 

 Ill, Fig, 11) which is much like this. The whole aspect of 

 the hypostome of the Gonionema polyp is very similar to 

 that of the manubrium of the young medusa (Fig, 26), The 

 ectodexTn at the edges of the mouth becomes thickened and 

 armed with nematocysts, which have by this time appeared, 

 in the manner to be described later, over much of the body 

 of the hj/dra. Below the mouth, the hypostome becomes nar- 



