SP0NGE-SPICULES. 117 



little round green seed-vessels during the time that the fruit is in 

 season. That they clung so tightly as not to be removed without 

 difficulty, we all knew, but we did not all know the cause. The 

 magnifying-glass, however, reveals the secret at once. The 

 whole of the surface is covered with little sharp prickles, 

 curved like hooks, and turned in all directions, so that, however 

 it may be thrown, some of them are sure to catch. 



So readily do these hooks hold to anything which they 

 touch, that if a lady only sweeps her dress against a plant of 

 Goose-grass, she is sure to carry off a considerable number of 

 the seed-vessels, and to waste much time afterwards in picking 

 them off. 



The seed-vessel of the common Burdock, known popularly 

 by the name of Bur, is armed in a similar manner, but, as it 

 is much larger, it is easily avoided. Sheep suffer greatly from 

 burs, which twist themselves among the wool so firmly that it 

 is hardly possible to remove them without cutting away bur 

 and wool together. As to a Skye terrier, when once he gets 

 among burs, his life is a misery to him (I was going to say, a 

 burden to him, but it would have looked like a pun). 



Below, and on the left of the Gralium-seed, are some spicules 

 of the Hymedesmia, a sponge which is found on the coast of 

 Madeira. The following account of it occurs in the Intel- 

 lectual Observer , vol. ii. p. 312 : — 



" Fish-hook Spicule. — We have received from Mr. Baker, 

 of Holborn, a slide containing spicules of the Hymedesmia 

 Johnsonii, which are stated to be rare objects in this country. 

 They have the form of a double fish-hook, and on the inner 

 surface of each hook is an extremely sharp knife-edge pro- 

 jection, corresponding with a similar and equally sharp 

 projection from the inside of the shank. 



" These minute knife-blades are so arranged that in addition 

 to their cutting properties, they would act as barbs, obstructing 

 the withdrawal of the hook. The two hooks attached to one 

 shank are not in the same place, but nearly at right angles 

 with one another, so that when one is horizontal the other is 

 vertical, or nearly so. A magnification of four or five hundred 

 linear does not in any way detract from the sharp appearance 

 of the knife-edges, and they may take their place with the 



