168 PKOF, T. E. JONES — IMrORTANCE OF 



of a sponge made up of long spicules ending with three prongs. 

 Here are diagratns of anchor-like and other spicules, some double- 

 anchored, some club-shaped, pin- shaped, etc. "When the sponges 

 die, these mineral spicules do not cease to exist ; they lie about in 

 the sea, especially if siliceous, and form beds of material like 

 sandstone. Here in a little bottle are some spicules from the 

 Upper Greensand of Devonshire. There is not merely a thimbleful 

 or a handful — there are square miles of it. Other beds made of 

 spicules are to be found at Folkestone, and in the Isle of Wight, and 

 elsewhere. So also you can hardly break a flint without seeing 

 the spicules. It was once so much chalk, and retains whatever 

 organisms were present in it originally. Not only in these Creta- 

 ceous beds, but in the Silurian rocks there are fossil sponges 

 recognizable by the shape of their minute spicules. Spicules among 

 other minute organisms have been found in the ooze of the Atlantic 

 and other oceans, thousands of feet deep. This was one of 

 Ehrenberg's discoveries. Very many scientific people have made 

 and studied deep-sea soundings besides the voyagers in the " Chal- 

 lenger ; " but the "Challenger" takes over much credit because 

 the Expedition happened lately, and the public have heard much 

 about it. One of the most useful results of the fossilization of 

 sponges is that they lead to the formation of a kind of flint, called 

 chert, made up of the spicules cemented together into a granular 

 but somewhat translucent rock. It is useful for road-stone, for 

 instance in Sm-rey, and whetstones for scythes were formerly made 

 from the chert of the Blackdowns in Devon. 



Amongst the marine animalcula which have hard material in 

 their tissue or substance, probably none are more durable than the 

 Polycystina. Many of you have specimens from Barbadoes, I have 

 no doubt. They are washed with care, and then show most beauti- 

 ful basket-work, such as Chinese carving cannot surpass. Many 

 of these Polycystina are globular, with globe-within-globe of 

 beautiful fenestrated, or lattice-like, basket-work. The " Chal- 

 lenger" expedition found that they abound more over some oceanic 

 areas than at others. They occur in the fossil state ; at Springfield 

 in Barbadoes there is a very considerable stratum, extending 

 several miles ; they occur also in the Cretaceous rocks of Germany. 



Then there is another set of creatures — the small bivalved Ento- 

 mostraca. They are representative members of an enormous family, 

 belonging to the Crustacea. 



In this group of creatures there are several, essentially similar in 

 body and limbs, but still very ditterent in appearance. There is 

 the little Branchipus, not inclosed in a shell, but showing all its 

 numerous segments and their foliaccous appendages, whereby the 

 creature moves in the water and obtains oxygen from the water. 

 The Cyclops has a jointed horny armour from head to tail. The 

 next little Entomostracan we can notice is Baplmia index, the 

 water-flea, so called because it darts about in the water with a 

 jerky movement as a flea jumps elsewhere ; and it is thus put 

 down among the best known of little jumpers, according to the 



