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GRANTIA. 

 A Sponge of the Sycon type. 



Write a short Description of the Sycon Sponge (Grantia), 

 showing the Structured Difference between it and 

 one of the Ascon Type. 



Grantia is sac-shaped but flattened. The wall is perforated 

 by numerous minute inhalent pores, and there is a large 

 exhalent osculum. The base of the cup has sometimes 

 a short stalk which serves for attachment to seaweeds 

 and rock-surfaces. 



The internal gastral cavity of this sycon sponge is lined 

 with thin flat epithelial cells, and it has a number of pouches 

 formed by infoldings of the wall. These are called radiating 

 chambers and the choanocytes are confined to them. 



The inhalent canals are in communication with these 

 radiating chambers, and the opening of communication 

 between a canal and a chamber is termed the prosopyle. 



In the ascon type (e.g., Leucosolenia) the wall is not 

 folded, there are no radiating chambers, and the internal 

 gastral cavity is lined throughout with choanocytes. 



The short inhalent canals are in direct communication 

 with the internal gastral cavity, and the opening of an 

 inhalent canal into the central cavity is the prosopyle. 



Sponge Development. 

 How do Sponges multiply ? 



By vegetative budding the individual or colony is in- 

 creased ; but the mode of reproduction of the species is 

 sexual, the sperms and ova being developed (both in the 

 same sponge, in some instances) from genital cells (amce- 

 bocytes). 



In the freshwater sponge, Spongilla, unfavourable con- 

 ditions are tided over by the development of gemmules or 

 statoblasts, which are formed by the grouping together of 

 food-laden cells. 



