IIARDWICKE'S SCIENCE-GOSSIP. 



179 



and far-seen colour) in order to make up some tone of 

 purple. Among the violets, also, we have a tendency 

 to purple and even white varieties, instead of a fixed 

 determination to stick to blue; as if'the latter colour 

 had been found not to answer. Those polypetalous 

 flowers which have most faithfully adhered to a blue 

 colour (as regards our British flora) are included in 

 Linacere. The milkwort is usually called blue, and its 

 blue is of a dark and lovely colour ; but every one 

 knows that this plant bears pink and white varieties, 

 in some places quite as commonly as the normal blue 

 flowers. On the other hand, we find that among the 

 gamopetalous division of our British flowering plants, 

 no fewer than fifty-seven species (against ten of the 

 polypetalous) are decidedly blue. In addition, there is 

 quite a host of which I have taken no statistical heed, 

 marked "lilac," "purplish," etc., in which blue is 

 a colouring agent. Of the gamopetalous orders Bor- 

 aginacese and Campanulaceae are the most conspicuous, 

 the latter bearing little besides blue flowers and 

 possessing corollas of the most typically gamope- 

 talous character. Of course polypetalous flowers are 

 visited by butterflies as well as bees, and it would be 

 interesting to note if the former, rather than the 

 latter, picked out the blue kinds. I only offer these 

 remarks as tentative. Is there anything in them ? — 

 J. E. Taylor. 



OUR COMMON BRITISH FOSSILS, AND 

 WHERE TO FIND THEM. 



No. VIII. 



By J. E. Taylor, Ph.D., F.L.S., F.G.S., &c. 



WE have already seen that, to a great extent, 

 Encrinites occupy the place in the rocks of 

 the Palaeozoic epoch which sea-urchins and their 

 allies do in the Secondary strata, and in the seas of 

 the present day. The sea-urchins proper are more 

 abundant now than at any previous period in the 

 world's history. They inhabit every sea, and almost 

 every shallow and depth in the seas. More than at 

 any other time one modern group of them (the Echini) 

 merit the name of Echinodermata, or "spiny- 

 skinned," given to the entire order. The common 

 sea-urchins, such as Echinus csculcnta or E. miliaris, 

 are covered with what are not inaptly called "spines." 

 The Echinodermata are doubly important, on 

 account of their numerical abundance and wide distri- 

 bution in the seas of the present day, and their 

 great geological antiquity. We have already noted 

 their general persistence in the rocks of every geological 

 epoch since the Silurian up to our own, and that we 

 find their species and types increasing in number in 

 proportion as we approach the present epoch. The 

 common Sea-urchin {Echinus miliaris) is a familiar 

 example. It well deserves its name, for, when alive, 

 it is so thickly covered with spines, as to greatly 



resemble the common hedgehog ; when dead, these 

 spines peel off, and then the surface is seen covered 

 with minute knobs or tubercles, to each of which a 

 moveable spine was attached, on the principle of the 

 ball-and-socket joint. The shell is composed of car- 

 bonate of lime, and is made up of an innumerable 

 number of separate pieces, all of which are mosaicked 

 together. No fewer than six hundred of these go 

 to make up the entire " test," as the shell is techni- 

 cally called. And yet, although in the adult state 

 it may be several inches in diameter, the shell has 

 not been moulted since the animal was no bigger 

 than a pea ! There is a membrane lining the ex- 

 terior of the test or shell, and this has the power of 

 secreting the carbonate of lime diffused through sea- 

 water. As the membrane is inserted between every 

 one of the six hundred and more plates, it is able to 

 add lime along the edges of each, and thus the whole 

 structure grows out uniformly and symmetrically, 

 almost like the expanding of a bubble when blown 

 out. A more beautiful architectural contrivance could 

 not be imagined than is thus furnished to us by this 

 insignificant creature ! 



Take one of the rounded tests you may have 

 picked up at the sea-side, out of which the animal 

 has been removed, and hold it up so that the 

 light may be seen through it. Besides the large 

 apertures at the top and the bottom (anus and mouth) 

 you perceive rows of minute punctures radiating down 

 from the summit to the base. These punctures are 

 called "ambulacral pores," and the plates (of which 

 there are five rows) in which the pores occur are 

 termed "ambulacral plates," for a reason that will 

 shortly be seen. In addition to these, there is a 

 plate specially perforated, called the ' ' madreporiform 

 tubercle " (on account of its being as porous and 

 spongy as the common Madrepore coral), and its 

 office seems to be to admit the sea- water as a 

 filter. From this a sort of canal proceeds internally 

 to a tube which surrounds the gullet at the base 

 of the shell or test like a ring. From this 

 circular canal there radiate, like the arms of a 

 star-fish, certain other canals which pass in front 

 of the rows of perforated plates, and meet together 

 at the top. Each of these five canals gives off in its 

 course innumerable tubes, which can be protruded 

 through the little punctures at the will of the animal. 

 At the base of each little water-tube, on the other 

 side of the canal, is a little water-bag, and when 

 this is compressed (as when a boy squeezes a 

 hollow indiarubber ball he has first filled with water) 

 the minute water-tubes, or "ambulacra," are 

 lengthened even beyond the spines of the animal. 

 Myriads of them can thus be protruded whenever the 

 sea-urchin thinks fit, and they may then be seen 

 wriggling and moving about like so many worms. 

 At the base of each is a sucker, and so, when a few 

 scores of the "ambulacra" are thrust forth, and have 

 attached themselves to any object, they are enabled to 



