GENERAL ZOOLOGY 



Osculum 



Porocyte 



Fig. 9.8. Diagrammatic longi- 

 tudinal section of an asconoid 

 sponge. (Adapted from L. H. 

 Hyman, The Invertebrates: Protozoa 

 through Ctenophora, copyright 1940 

 by McGraw-Hill Book Co., Inc., 

 printed by permission.) 



Spicules 



here. These are considered totipotent cells and have been described as cap- 

 able of differentiating into all the other cell types, including gametes. 



More Complex Sponges. The simplest adult sponges, such as Leucosolema, 

 arise by budding and growth from an olynthus. More complex sponges are 

 modified in a great variety of ways, but their units of organization, the canal 

 systems, can be derived from a type like the olynthus. A series of these modi- 

 fications is shown diagrammatically in Figure 9.10. The primary type of 

 canal system found in the olynthus is termed the asconoid type. A second 

 type, called syconoid, found in such sponges as Scypha, is actually derived 

 in development by the folding of the wall of an olynthus stage and subsequent 

 differentiation. Additional cavities are thus formed within the sponge, and 

 the course of water from the exterior to the osculum becomes more com- 

 plicated. The openings in the surface of Scypha are not the same as the pores 

 of the olynthus, which correspond rather to those leading from the so-called 

 incurrent canals to the excurrent canals. In the adult Scypha these pores 

 are no longer intracellular channels; the porocytes of the olynthus stage dis- 

 appear during development. Other changes involve the restriction of the 



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