202 



HARDWICKE'S SCIENCE-GOSSIP. 



[Seft. 1, 1868. 



In Helicella cellaria the dental formula is 



17.1 17 



" The central plate is very long and narrow, with 

 three teeth, occupying nearly the centre of the 

 plate; the first four laterals are irregular in shape, 

 apparently bidentated ; the uncini are long, single, 

 and aculeate" (see fig. 212). 





s 



Fig. 211. Part of the lingual ribbon of Testacella haliotidea 



The lingual teeth of the "amber snails" are like 

 those of Helix ; in Succinea pzitris, the formula is 



Fig. 212. Part of lingual ribbon of Helicella cellaria. 



^jjjp ; the central tooth differs only from the la- 

 terals in size : the teeth are three-lobed, the central 

 is large (fig. 213). 



Fig. 213. A transverse row of the lingual ribbon of 

 Succinea putris. 



The dental formula of Limneea stagnalis is 



551.55 

 110 



= 12*210. The central tooth is very minute; the 

 laterals are large, with two unequal prominent 

 points, the outer the smallest. 



In Ancyclus fluviatilis the lingual dentition pre- 

 sents the following characters : — The central tooth is 

 minute; the lateral teeth, thirty-seven in number, 

 have long recurved hooks, and are at first simple, 

 but becoming ultimately narrowed and minutely 

 toothed ; there are 120 transverse rows. 



Fig. 



214. Portion of a transverse row of the lingual ribbon 

 of Ancyclus fluviatilis. 



In the subgeneric group Velletia, Gray, the 

 lingual dentition is different, tiie central part of each 

 row being much arched, and composed of a central 

 tooth, with twelve similar laterals on each side, next 

 to which is a tooth of a different form, and lastly, 

 six more on eacli side, which latter are in a slight 

 curve ; the number of transverse rows is 75 ; the 

 total number of teeth is 29,215.— Tate's Mollusks. 



AGE OP TREES. 



rFIHE life of a plant is determined by its inner 

 -*- structure, by the laws of its growth, by i its 

 power of resisting external injuries, and by other 

 circumstances, many of which are a mystery, and 

 no doubt will ever remain so. But, 

 bounded though it is within limits as 

 narrow and precise as those which hedge 

 round the life of man or the lower 

 animals, there are cases on record of 

 certain members of the vegetable king- 

 dom, whose existence has been prolonged 

 for very extraordinary periods. 



The most celebrated of all old trees 

 (and perhaps the most curious, from its 

 belonging to the endogenous division, which does not 

 generally boast of long-lived members) is the Great 

 Dragon-tree of Orotova, in Teneriffe. This mon- 

 strous specimen, which came to an untimely end in a 

 hurricane a few months ago, was well known and 

 carefully looked after at the conquest of the island 

 by De Bethencourt in the year 1102. It appears to 

 have been of the same size and appearance then as 

 now — viz., from 70 toSOfeet high, with a hollow trunk 

 of about 20 feet in diameter,— whence, judging from 

 the slowness of growth in this family of plants, and 

 the little change that has taken place in fourcentu- 

 ries and a half, it is inferred that the tree could not 

 have been less than 5,000 years old at the time of 

 its death. Another giant among the pigmies of 

 modem days is the Baobab (Adansonia), an African 

 tree, specimens of which, growing on the banks of 

 the Senegal river, 60 to 80 feet high and 30 feet in 

 diameter, were estimated by Adanson to be over 

 5,000 years old. The Portuguese, on their voyages 

 of discovery, were in the habit of carving their 

 names, &c, on conspicuous trees, as a memorial of 

 their having been, the first to visit the spot. 

 Adanson arrived at the age of the trees by com- 

 paring the depth of the indentations with the 

 number of " rings " in the portion of wood over- 

 growing them. The names themselves bore a date, 

 which showed them to have been cut three centuries 

 prior to his visit. It has been suggested that pos- 

 sibly in a tropical climate these rings may not be so 

 good a test of age as in our more temperate clime, 

 where they are really annual. Nevertheless, allow- 

 ing that the Baobab forms two rings in each year, 

 in lieu of one, it is still deserving of " honourable 

 mention." Yews have a great reputation as long- 

 livers. The care usually taken of them in church- 

 yards and similar places no doubt tends greatly to 

 their preservation. Thus a Yew in the churchyard 

 of Brabourne, in Kent, has, it is believed, reached 

 the enormous age of 3,000 years ; another at Fortin- 

 gal, in Scotland, is quoted at 2,600 years, and 

 others at Crowhurst, in Surrey, and at Fountains 

 Abbey, are put down at 1,400 years. The Yew has 



