SPONGE WEAVERS. 115 



there is every gradation. Some of the forms are 

 certainly elegant, being branched and forked like a, 

 stag's horn, but these perhaps are rather exceptional 

 species, since the majority present, especially in the 

 living state, little that is attractive in appearance. 

 Their beauties must rather be sought in their micro- 

 scopical structure, and the elaborate interweaving of 

 the skeleton. It is probably on account of their 

 unattractive appearance that they have had so few 

 students, except here and there a plodding enthusiast, 

 like our own Dr. Bowerbank and Dr. Carter ; in 

 fact, at almost any time during the past century 

 those who pursued the study of sponges in these 

 islands could be counted on the ringers of one hand. 

 Of course, there are difficulties to be overcome, 

 and one of these is the observation of specimens 

 in the living state, for which purpose dredging must 

 be resorted to, and such physical exertion as 

 hardly commends itself to the majority of modern 

 naturalists. 



In order to give some general idea of sponge 

 structure we must commence with the skeleton, but, 

 before doing so, it will be necessary to explain what 

 is meant by sponge " spicules," which are the element 

 of which the skeleton in most sponges is mainly 

 composed (fig. 16). If a fragment of siliceous or flinty 

 sponge is boiled in nitric acid, all the fleshy portion 

 is destroyed, whilst the flinty, or siliceous, remains 



I 2 



