100 H. GILBEETSON NOTES ON SPONGES, 



and the cilia themselves well defined, more especially when the 

 gemmule leaves the parent, and swims freely in the water, after a 

 time settling down and producing a new sponge. 



Sponges are also propagated by spontaneous division of the 

 sarcode. 



Great discussion has taken place in former years as to whether 

 sponges were animals or vegetables, but from the foregoing re- 

 marks you will readily understand how it comes to pass that they 

 are now classed among animals, though of a very low type. It 

 may be interesting to note in further confirmation of the theory of 

 the animality of sponges that from chemical analysis the composi- 

 tion of their elastic fibrous skeleton is found to be very similar to 

 that of silk. Lehmann* says that Mulder considers from the re- 

 searches of Croockwit that the common sponge consists of twenty 

 atoms of fibroin, one atom of iodine, three atoms of sulphur, and 

 five atoms of phosphorus, and that "Its chemical constitution 

 affords one of the arguments why the Spo7igia should be classed 

 amongst animals and not amongst plants, since in the vegetable 

 kingdom we nowhere meet with a substance in the slightest degree 

 resembling fibroin." 



Let us now turn to the fossil sponges commonly called flints. There 

 are two sources from which we obtain flints in our neighbourhood, 

 viz. the chalk and the gravels ; there is, however, no doubt but 

 that all our flints came originally from the chalk, and that our 

 gravel beds chiefly consist of flints which, having been washed out 

 of the chalk by the action of rivers, glaciers, or the sea, have also 

 by the same agents been more or less broken up and worn down 

 by attrition. 



That most of these flints owe their origin to sponges or allied 

 forms of animal life, I gather to a great extent by their outward 

 appearance, in very many instances greatly resembling recent 

 sponges, and also from the fact that if a thin fragment of any flint 

 properly prepared be subjected to microscopic examination, either a 

 foraminifer or the spore of an alga, or some other organism, is sure 

 to be found in a similar manner to that in which such organisms 

 are found in recent sponges. 



The flints which I exhibit show in a remarkable manner that 

 they are simply silicifled sponges. As has been already stated, 

 sponges have, at a certain stage of their existence, the power of 

 locomotion — viz. at the time the gemmules leave the parent, when, 

 by the action of cilia, they freely swim about until they meet with 

 some obstacle and settle down upon it, or get into some quiet 

 cranny of a rock or some empty shell. Of the latter we have many 

 examples among these flints. Here is a piece of Inoceramus, a shell 

 very abundant in the Chalk, about three inches and a half long by 

 two inches wide, with a small flint attached to it, having an oval 

 base, with a diameter of half an inch by a quarter, and a height of 

 haK an inch. This small specimen shows one large excurrent orifice 



* 'Physiological Chemistry ' (Cavendish Society's edition), vol. i, p. 401. 



