io Invertebrate Zoology, 



which cannot be seen at present. Do you find anything 

 that might strain the water as it enters the mcurrent canals ? 

 Do the buds communicate freely with the cloaca of the 

 parent ? 



Examine with lowest power of compound microscope. 

 The outer lighter-colored layer of the sponge is now seen 

 to be made up of innumerable, needle-like spicules, while 

 the inner portion is supported by radiate spicules. 



Make enlarged drawings of the parts thus far considered. 



Cut a thin transverse section of a dry sponge and note 

 the radial canals, and the smaller and also straight incurrent 

 canals lying parallel with them. Are the needle-like spicules 

 arranged more abundantly over the peripheral ends of the 

 radial canals ? v j Note the arrangement of the triradiate 

 spicules in the walls of the tubes. T-shaped spicules are 

 arranged around the cloacal chamber, each sending one ray 

 into the cavity. Recall the spicules of the Ascon. Do any 

 of the incurrent canals pass through the wall of the sponge 

 from the periphery to the cloacal chamber? 



Make a drawing showing the arrangement of the spicules. 



Examine now a specimen that has been decalcified, stained 

 and cut into transverse sections by means of a microtome. 

 The spicules will not be present though their surrounding 

 mesodermal cells will appear as a delicate nucleated retic- 

 ulurn extending between the parallel tubes and into pyram- 

 idal masses at the peripheral ends of the radial canals. 

 Endodermal cells, as a single layer, line the cloacal chamber 

 and the radial canals ; but while the cells of the former are 

 flattened out and form a " pavement epithelium," those of 

 the radial canals retain the flagella and collars present in 

 the Ascon, and by their activity induce the circulation of 

 sea-water. Note that the incurrent canals are lined with 



