1 88 



PHYLUM CCELENTERA 



this process there are formed first two and then four diverticula of the 

 general cavity, which are arranged round the gullet above, and open 

 freely into the digestive cavity below. In the gullet region these are 

 separated by broad septa, which are continued into the lower region of 

 the body as four interradial ridges or taeniolae. The tentacles bud out 

 from the region of the mouth, the first four corresponding in position to 

 the four pouches. Interradially above the four septa, four narrow 

 funnel-shaped invaginations arise ; these are produced by the ingrowth 

 of ectoderm, which then forms the muscle fibres which run down the 



Fig. 95. — Diagram of life-history of Aurelia. — After 



Haeckel. 



I, Free-swimming embryo ; 2-6, various stages of Hydra-tuba ; 

 7. 8, Strobila stage ; 9, liberation of Ephytje ; 10, 1 1 

 growth of Ephyrae into Medusae. 



taeniolee (contrast the endodermic muscles of Anthozoa). In contrasting 

 this development with that of the hydroid polyp, Goette specially 

 emphasises the fact that the radial symmetry is first indicated by the 

 gut pockets, and the tentacles are late in development. Goette 

 describes a quite similar process of development in certain sea- 

 anemones, and claims to have found there rudiments of septal pockets 

 and ectodermal muscles, thus confirming his view of the intimate 

 relation between the Anthozoa and Scyphomedusae. 



The larva now forms a " Hydra-tuba " or " Scyphistoma " , it is 

 about an eighth of an inch in height. By lateral budding, or by the 

 formation of creeping stolons, it may give rise to larvas like itself. 



