TKHbat 16 a Sponge? 169 



product. If we burn a piece of sponge it ex- 

 hibits very much the same phenomena as the 

 burning of hair or wool, and the smell is very 

 much the same. 



The structure of a piece of sponge when 

 examined under a microscope is a wonderfully 

 complicated fabric. Under the microscope it 

 shows a network of interlacing filaments run- 

 ning in every direction in a system of curved 

 lines intersecting and interlacing with each 

 other in a manner to leave capillary openings. 



It is a wonderful structure, and one that a 

 mechanical engineer could get many valuable 

 lessons from. It will stand a strain in one 

 direction as well as another. There are no 

 special laminations or lines of cleavage; it is 

 very resilient or elastic, and readily yields to 

 pressure, but as readily comes back to its nor- 

 mal position when the pressure Is relieved. If 

 we examine the body of a sponge we shall 

 notice that there are occasional large openings 

 into it, but everywhere surrounded by smaller 

 ones. If we should capture a live sponge and 

 place it in an aquarium with sea water, where 

 we could study it, we should find a circulation 

 constantly going on, and that water was con- 

 stantly sucked in at the smaller openings all 

 over the outside of the sponge and as continu- 

 ously ejected from the large openings. This 

 process constitutes what corresponds in the 

 higher order of animals to both respiration 



