HYDR^E, JELLYFISHES, SEA ANEM(_)NES, CORAL POLYPS 53 



floating on the surface of the sea (Fig. 19). In the center 



of the under surface of tire l)ocly is tlie mouth. Abo\'e 



the mouth is the stomach, 



and higher up, from the end 



of the digesti\'e cavity, canals 



radiate like the ril)s of an 



umbrella. These canals exten( I 



downward along the insi<le of 



the dome and finalh' eoni- 



nrmricate with a circular canal 



around the edge of the disk. 



This system of tubes is suggestive of the water vascular 



system of the echinoderms. 



Aureha has an interesting and complex Ufe history. The 

 adult produces eggs, each of which hatches mto a ciUated 



Fig. 20.- 



- Embryo of jellyfi.sll 

 (AurcUa) . 



Fig. 21. — Hydralike .stasi- of .\urclia. After Aga,ssiz. 



embryo (Fig. 20). The embryo soon attaches it.self to a 

 rock and transforms to a hydrahke animal about one half 



