EXTANT GASTR^ADS. ^y 



of Haliphyseinia forms a most simple, cylindrical or eo-o-- 

 shaped pouch, the wall of which consists of two cell-strata. 

 The cavity of the pouch is the stomach -cavity, and the 



Ftgs. 180, 181. — Baliphysema primordiale, an extant Gastraea-forra. 

 Fig. 180. External view of the whole spindle-shaped animal (attached by 

 il^s foot to seaweed). Fig. 181. Longitudinal section of the same. The 

 primitive intestine (d) opens at its upper end in the primitive mouth (»'). 

 Between the whip-cells (g) lie amoeboid eggs (e). The skin -layer (h) below 

 is encrusted with grains of sand, above with sponge-spicules. 



opening at the top is the mouth-opening (Fig. 181, m). 

 The two cell-strata forming the wall of the pouch are the 



