I04 



PORIFERA. 



Fig. 38— Calcareous Tri- 

 RADiATE Spicules of 

 Sycandra [GraiiHa). 



Highly magnified. 



acid. They are found to be 

 calcareous in nature. They sup- 

 port the wall of the sponge and 

 form its skeleton. The further 

 structure of Sycandra must be 

 followed by prepared microscopic 

 sections or by teasing to pieces 

 and examination with the micro- 

 scope. A transverse section as 

 seen with low powers is shown 

 in Fig. 39. The wall here shows 



Fig. 39.— Transverse Section of a Sycandra {A Sycon). 



Prosopyle. 



Inhalent Canal. 

 The central cavity is the paragastric cavity. 



a number of radial canals, some of them with thick 

 walls and others with thin. The former open into 

 the paragastric cavity by small contracted apertures and 

 are called exhalenf canals, whilst the latter open by the 

 pores to the exterior and are termed inhalent canals. 

 Further examination would show that the two sets of canals 



