CALCAREOUS SPONGE. 27 



in the box, fill with the hot paraffine, and allow it to cool. 

 Cut a number of sections as thin as possible across the 

 imbedded sponge with a sharp i-azor, and transfer them to 

 a glass slide. Cover them with a mixture of equal parts 

 of carbolic acid and turpentine to dissolve away the par- 

 affine. After the sections become transparent, remove as 

 much as possible of the carbolic acid and turpentine with 

 a piece of blotting-paper, and cover them with a drop of 

 Canada balsam, and cover with a thin glass cover. The 

 balsam should be kept in a wide-mouthed bottle, loosely 

 covered by a perforated cork, through which a glass-rod 

 has been passed, and it should be taken up on the rod, 

 and thus transferred to the slide. If the balsam is too stiff 

 to drop readily from the rod, it may be liquefied by adding 

 a small quantity of benzole. The carbolic acid and tur- 

 pentine should also be kept in a bottle with a glass rod 

 passed through the cork. 



a. Examine the longitudinal sections with a power of 

 two or three hundred diameters, and note : — 



1 . The cut sections of the radiating tubes ; circular when 

 cut perpendicular to their long axis. 



2. The more common kind of triradiate spicules ar- 

 ranged around, and in the spaces between, the tubes. 



3. The long needle-like spicules upon the ouier surface. 



4. Make a sketch of a longitudinal section. 



h. Examine a transverse section with the same power, 

 and notice ; — 



1. The radiating tubes (Fig. 14, h, 5, b) laid open 

 longitudinally. Each tube is divisible into three regions : 



(i.) The narrow, inner aperture, through which its cav- 

 ity communicates Avith the cloaca. 



(ii.) The long cylindrical canal, which traverses the 

 sponge-flesh from its outer surface to the cloaca. 



