74 



INVEKTEBKATA 



CHAP. 



relatively small. This 



FIG. 53. AstrobilizedScyphis- 

 tonia of Aurelia aurita. 

 (After Glaus.) 



7, forked lappet of edge of disc 

 of Ephyra ; ten, tentacles of Hydra- 

 tuba degenerating ; Jen 1 , rudi- 

 mentary sense-tentacles of Ephyra. 



again is a feature which we find in many 

 larvae which are adapted for continuous 

 free-swimming life. The larva never fixes 

 itself, and eventually the lobes of the Ephyra 

 grow out in a circle round the mouth. 

 The whole development is therefore modified 

 along quite similar lines to those exhibited 

 by the Geryonidae, the hydra-tuba being 

 modified into a floating larva, just as is the 

 hydroid stage of the Geryonidae. 



When we review what we have learned 

 of the development of Scyphozoa, we are 

 struck at first by the great differences 

 between their life-histories and those of the 

 Hydrozoa. A deeper and closer analysis 

 tends, however, to diminish the supposed 

 differences very much. It has been shown 

 that many Hydroid colonies periodically 

 lose and regenerate the "polyps" (Allman, 

 1871-2), (i.e. the swollen distal ends or heads 

 of the hydroids which carry the tentacles 

 and genital organs), that during the winter 

 the polyps are often absent, and that these 

 are regenerated from the basal stumps in 



FIG. 54. An Ephyra larva of Aurelia aurita just after liberation from the strobilized 



scyphistoma. (After Friedemami. ) 



ad, adradial lobe of ring-gut ; </./, gastral filament; int, inter-radial lobe of ring-sinus ; /, forked 

 lappet of edge of disc ; o.c, oral cone ; per, per-radial lobe of ring-sinus ; r, ring-sinus ; sg, sub-genital 

 pit ; toil, sense-tentacles. 



