HANDBOOK OF INVERTEBRATE ZOOLOGY. 



b. The oKmlnm, or wide, round opening (Fig. 13, 6), 

 through which the cloaca communicates with the exterior. 



FIG. 13. Longitudinal 

 section of a calcareous 

 sponge (Sycandra ciliata) 

 magnified about ten diame- 

 ters. (Drawn from nature 

 by \V. K. Brooks.) 



A. Mature sponge. 

 B. Bud. a. Crown of large 

 spicules around osculum. 

 b. Osculum. ft 1 . Osculum 

 of bud. c. Layer of spic- 

 ules. shown in a part of the 

 figure only. <1. Radiating 

 t ulics. shown in a part of the 

 figure only. e. Inner or 

 cloacal apertures of the ra- 

 diating tubes, shown in part 

 of the figure only. /. Sponge 

 flesh. (/. Cloaca. g l . Cloaca 

 of bud. fi. Base or attached 

 surface of sponge. 



c. The wall of the 

 cloaca, as shown by 

 the section, is made 

 up of : 



1. An outer, brown 

 layer (Fig. 13, c), 

 which a slight magni- 

 fying power shows to 

 be made up of the pro- 

 jecting ends of the cal- 

 careous needles or spicules which form the skeleton of the 

 sponge. 



2. An inner, nearly white, layer : the sponge-flesh (Fig. 

 13,/). This layer is somewhat thicker than the outer 



