96 



COLLEGE ZOOLOGY 



Central cavity 

 Surface pore 



Flagellated 

 chamber 



RHAGON 



Figure 48. Types of canal systems of sponges; diagrammatic sections. The sycon type is 

 derived, theoretically, by the outpushing of the wall of the ascon type of sponge into saclike 

 chambers. Note how much each chamber of the sycon type of sponge resembles the single 

 chamber of a simple sponge. The rhagon type, like the bath sponge, is more complex with an 

 elaborate system of canals and flagellated chambers. The arrows indicate the course of water 

 through the various types of sponges. (Ascon and sycon types after Minchin; rhagon type after 

 Parker and Haswell.) 



is then enslieathed by an envelope of organic 

 matter like that composing the axial thread. 



Physiology 



Scypha lives on minute organisms and 

 small particles of organic matter drawn into 

 it by the back-and-forth beating of the 

 flagella on the choanocytes, but little or no 

 digestion occurs within choanocvtes. The 

 food particles are engulfed by amoebocytes 

 where they are digested. Digestion, as in a 

 protozoan, is intracellular. Distribution of 

 the nutriment is accomplished by diffusion 

 of digested food from cell to cell, aided by 

 the amoeboid wandering cells. 



Excretory matter is discharged through 

 the general body surface, assisted probably 



by the amoeboid wandering cells, and pos- 

 sibly by the collar cells. Respiration, like- 

 wise, takes place, in the absence of special 

 organs, by means of the cells of the body 

 wall. 



Sponges are usually considered to be very 

 quiet and sluggish, but actually they are 

 among the most active and energetic of all 

 animals, working night and day to create 

 the currents of water that bring food and 

 oxygen into the body and carry away waste 

 matter; they are veritable living dynamos. 

 The amount of water that passes through 

 the body of a sponge is tremendous; for ex- 

 ample, an average-sized sponge draws about 

 45 gallons of water through its canal system 

 in a single day. 



True nerve tissue in sponges has not been 



