BRANCH PORIFERA: THE SPONGES 91 



again, and the animal matter beaten, squeezed, or washed 

 out, leaving the cleaned skeleton ready for the market. 

 In this condition after being dried and sorted, they are 

 sold to the dealers, who have them trimmed, re-sorted 

 and put up in bales or on strings ready for exportation. 

 There are many modifications of these processes in differ- 

 ent places, but in a general way these are the essentia- 

 steps through which the sponge passes before it is con- 

 sidered suitable for domestic purposes. Bleaching- 

 powders or acids are sometimes used to lighten the color, 

 but these unless very delicately handled injure the dura- 

 bility of the fibres." 



Classification. The sponges are classified according 

 to the character of the skeleton. In one group are put 

 all those sponges which have a skeleton of calcareous 

 spicules, and this group is called the Calcarea. All other 

 sponges are grouped as Non-Calcarea, the members of 

 this group either having no skeleton at all, or having a 

 skeleton composed of siliceous spicules or of spongin 

 fibres. According to the absence or presence of a skele- 

 ton and the character of the skeleton when it exists the 

 Non-Calcarea are subdivided into smaller groups. 



