ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



with its supplies of oxygen into close proximity to the gonad the lower 

 surface of the umbrella is tucked inwards to form a subgenital pit 

 (Fig. 44, I, s.p), which remains freely open to the sea-water by a wide 

 circular opening while the roof, separating it from the stomach and giving 

 rise to the gonad on its upper or gastral surface, is comparatively thin. 

 The gonad takes on as already mentioned a bright purple colour and the 



at: 



77C. 



Fig. 42. 



Aurelia, young specimen viewed from below, x 16. g.f, Group of gastral filaments- m, manu- 

 brium with mouth opening at tip ; r, ring canal ; r,c, radial canal ; s,t, sensory tentacle ; st, stomach. 

 [In the young specimen the angles of the manubrium have not yet grown out into long arms ; 

 the projecting pouches of the stomach and the gonads have not yet appeared ; and the branching 

 of the branched radial canals is not so complex as it is in the adult.] 



gametes shed from it pass into the cavity of the stomach and thence to 

 the exterior by the mouth opening. Within the curve of the gonad 

 there project from the floor of the stomach a row of somewhat tentacle- 

 like gastral filaments (Figs. 42 and 44, I, g.f). The endoderm covering 

 these is crowded with gland-cells which probably secrete digestive 

 ferment: their presence constitutes a characteristic feature of the 

 Acalephae. 



