38 



says — " The skeletons of poriferous animals consist of separate mi- 

 nute, earthy, crystalline spicula, connected together by a condensed, 

 elastic, cellular substance ; or of tubular elastic filaments of a horny 

 consistence. These parts are developed internally through the whole 

 cellular tissue of the body, and are often protruded through the sur- 

 face to protect the pores or the large vents. The earthy spicula in 

 most of these animals are siliceous, in many they are calcareous, and, 

 like the horny filaments of other species, they appear to be tubular, 

 like many natural crystals." Professor Rymer Jones, in his ' General 

 Outlines of the Animal Kingdom,' p. 14, says, — "Crystallized spicula 

 of this description form a feature in the structure of the sponge which 

 is common to many vegetables, resembling the formations called ra- 

 phides by botanical writers." 



I am not aware of the existence of any true crystals which naturally 

 present a central orifice similar to that of the general mass of the spi- 

 cula of sponges. The normal characters of a true crystallized body 

 appear to me to be solidity and angularity ; while, on the contrary, 

 the prevailing form of the earthy deposits in the animal kingdom is 

 that of the hollow cylinder. In this respect, therefore, the spicula of 

 sponges, whether they consist of siliceous or calcareous materials, al- 

 ways present themselves in the shape of a true cylinder, or of some 

 modification of that form. In further confirmation of the probability 

 of their animal origin, it may be stated that when siliceous spicula 

 are exposed for a considerable length of time to the action of the 

 blow-pipe, and then examined with a power of 500 linear, it is usu- 

 ally apparent that the internal tubular cavities of the spicula are coated 

 with a film of carbonaceous matter, strongly indicating the exis- 

 tence of a thin coating of animal substance within the spicula, (Pl.iii. 

 fig. 4 — 9). The external surfaces of the spicula also frequently ex- 

 hibit a carbonaceous filmy coat when incineration has not been con- 

 tinued too long, which gives them the appearance of having been co- 

 vered with a thin film analogous to the periosteum of true bone. 



The raphides, in many instances where I have had the opportunity 

 of observing them, have presented a truly crystallized and angular 

 form. They are solid, and, in no case that I have observed, cylindri- 

 cal like the spicula of sponges. Nor do these curious bodies occupy 

 the same relative situation in the plant that the spicula do in the 

 sponge. The latter are truly a portion of the organization of the ani- 

 mal, while the former can be considered but as a secretion deposited 

 in the cellular or inter-cellular structures of the plant. Under this 

 view, therefore, they cannot be adduced as a link connecting the 



