POMFERA 



33 



young stages of many sponges which afterwards, in their 

 adult condition, are much more complex. Owing to the 

 growth of the sponge-wall being unequal in different parts, 

 either folds or tube-like projections are formed, and these 

 subsequently become more or less completely fused, so 

 that the wall is much thickened (fig. 8) and is traversed 

 by canals which are really spaces enclosed between the 

 folds and outgrowths. In such forms the flagellated cells 



Fig. 8. Section of a portion of Grantia. Highly magnified. (From 

 Dendy.) 1. Openings of inhalent canals ; 2. Inhalent canal ; 

 3. Openings of inhalent canals into flagellated chamber ; 4. Flagel- 

 lated chamber; 5. Collar cells; 6. Spicules; 7. Exhalent opening 

 of flagellated chamber. 



are frequently confined to chambers in the sponge-wall 

 (fig. 8, 4). Canals, called incurrent or inhalent canals (2) ; 

 pass from the surface of the sponge to these chambers, and 

 others, the excurrent or exhalent canals, may lead from the 

 w. p. 3 



