98 mVERTEBUATE MORPHOLOGY. 



into sense-organs (Fig. 50, s) situated near the margin of the 

 bell and more or less enclosed in special chambers by the 

 growth around them of folds of the bell substance (Z). From 

 the centre of the subumbrella there hangs the manubrium 

 (m), the extremity of which is frequently prolonged into four 

 elongated mouth-lobes, and above it communicates with the 

 gastric cavity, g, which in simple forms extends to the 

 margin of the bell, being obliterated only at four interradial 

 points or lines. The four broad radial pouches thus produced 

 correspond with the radiating canals of the craspedote medu- 

 sae, and the line of fusion being imperfect at the margin of the 



Fig. 50. — Diagbam of Sctphomedusa. 

 g = gastric cavity. r = reproductive organs. 



I = lolie covering the sense-organ. s = sense-organ. 



m = month. tg — subgenital cavity. 



mf = mesenterial filaments. i = tentacle. 



bell a communication between adjacent pouches is present 

 comparable to the craspedote circular canal. This condition 

 is, however, only retained in the simpler forms ; in the higher 

 ScyphomedussB the lines or points of obliteration may be 

 omitted, and by secondary obliterations taking place over 

 various areas of the coelenteron, and by its irregular extension 

 towards the rim of the bell as this grows in diameter, a com- 

 plicated branching arrangement of the peripheral portion of 

 the coelenteron is produced, in which, however, the original 

 4-radial arrangement is as a rule distinctly indicated. Along 

 the interradial axes there are four deep depressions of the 

 subumbrellar surface, the funnds or subgenital chambers (Fig. 

 50, sg), above which lie the horseshoe-shaped reproductive 

 organs, r, developed in the coelenteric endoderm, one limb of 

 each horseshoe lying in each of the adjacent radial pouches. 



