54 



HARDWICKE'S SCIENCE -GOSSIP. 



[March 1, 1868. 



shade, the other parts of the tooth being of a rich 

 brown ; but in some specimens which I have by me 

 are of a bright amber hue. 



This form is very common in the TVealden, and 

 also in the lower greensand of the Cretaceous 

 System, the only difference being that those found 

 in the greensand are more of a brown colour ; but 

 otherwise in every particular identically the same 

 as those of the Oolite which lies below. These 

 teeth are fine objects for the microscope, and when 

 examining them, you might think, with very little 

 stretch of imagination, that you were looking at 

 some beautiful forest scenery. 



Fig. 40. Section of tooth magnified. 



Our intelligent gardeners who are employed to 

 lay out gentlemen's grounds, would receive valuable 

 hints, "nay ideas," in such employment. 



I think it will not be out of place here to refer 

 for comparison to the teeth of the existing shark 

 family ; and fig. 41 represents a tooth of the Squallus 

 or Blue Shark. 



Fig. 41. Tooth of 

 blue shark. 



Fig. 42. Section of shark's tooth. 



Fig. b on the dotted point of fig. 41, is that part 

 of the tooth which is attached to the cartilaginous 

 jaws of all the shark family; fig. 42 is a section at 

 the dotted point a of fig. 41 ; and fig. 43 is a section 

 at the point at b. This shark was caught by a friend 

 of mine only two years ago in the lied Sea. 



I may notice, for the benefit of learners, the method 

 I follow to prepare these teeth, either fossil or other- 

 wise, for the microscope, and which is simple enough . 

 Procure a piece of fine smooth slate, and a dish of 

 water; take the tooth and commence rubbing the flat 



side, keeping it under the water during the process, 

 until you have ground it down to its centre. Be sure 

 you have no scratches on the fine polished surface of 

 the article you are polishing ; then have a clean, clear 

 piece of ordinary glass, and hold it over a small jet 



Fig. 43. Section of shark tooth. 



with a little balsam on the centre of it, holding it 

 to the flame till the balsam bubbles and boils well ; 

 remove your glass from the flame, and watch the air 

 bubbles until they disappear; then place your 

 polished side on the balsam, which very soon sets 

 hard ; immerse it in the water in your dish again, 

 and rub away upon the slate the last side, until 

 sufficiently thin and transparent for the microscope. 

 Then fix a piece of glass on the polished section of 

 the specimen in the usual way, and it is ready for 

 inspection under your microscope. 

 South Shields. Joseph Weight, Jun. 



Planaria. — In Science-Gossip, for November, 

 1867, "E. T. Scott" inquires whether certain 

 animals observed in fresh-water, the one with two, 

 the other with four eyes, which "when touched 

 contract themselves into a hard lump, as a healthy 

 leech does," and which move in the same way — are 

 Planaria. In reply, we beg to inform him that the 

 Planaria have neither suckers, nor other visible 

 locomotive organs, but glide from one place to 

 another by means of innumerable cilia, with which 

 their bodies are clothed. In the commoner species, 

 the mouth is seated on the lower surface of the 

 body, nearer the tail than the head, and when they 

 feed they protrude from it a long trumpet-shaped 

 proboscis. The animals described by him are classed 

 with the leeches, and belong to the genus Glossi- 

 phonia (Johnson on the Medicinal Leech, 1816). 

 The one is a very common and active little species, 

 G. Hoc/data, which hatches its young in a kind of 

 marsupium, where they remain for some time. It 

 is a fearful sight to watch the mother and all her 

 cannibal brood feeding on some poor worm. The 

 other species is probably G. complanata, which has 

 four or six eyes. It is a more sluggish leech, and 

 does not carry the eggs about with it, but remains 

 over them while hatched, as a hen sits over her 

 eggs. — B. C. 



