EXTANT GASTILEADS. 



of Haliphysema, forms a most simple, cylindrical or egg- 

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

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



ff 



FIGS. 180, 181. Haliphysema primordiale, an extant Gastraea-form. 

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

 its foot to seaweed). Fig. 181. Longitudinal section of the same. The 

 primitive intestine (d) opens at its upper end in the primitive month (m). 

 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 



