DISCOVERY 



145 



the animal assumes its normal shape. For a time it 

 remains quiet, and then it begins slowly and feebly 

 to move about, and after a period which varies from 



Fig. I. — A T.\RDIGR.\DE. 



Highly magnified. 



{From Doyere.) 



a quarter of an hour to several hours, according to 

 the time its life has been suspended, the little animal 

 crawls away " on its lawful occasions." 



In the same sort of position, in gutters, amongst 

 moss, are another group of animals known as the 

 RoTiFER.\ or wheel-animalcules. These are creatures 

 of singular beauty which bear on their heads a number 

 of cilia whose rhythmic flickering produces an appear- 

 ance of a wheel going round. More than 200 years 

 ago Leeuwenhoek recorded the fact that these little 

 microscopic animals were also capable of drying up, 

 and resuming their normal activities when moisture 

 is again applied. As long ago as 1774-5 Mr. Baker, 

 in a letter addressed to the President of the Royal 

 Society, stated that the animal described " can, how- 

 ever, continue many Months out of Water, and dry as 

 Dust ; in which Condition its Shape is Globular, its 

 Bigness exceeds not a Grain of Sand, and no Signs of 

 Life appear. Notwithstanding, being put into Water, 

 in the Space of Half an Hour a languid ^Motion bogins, 

 the Globule turns itself about, lengthens by slow 

 Degrees, becomes in the Form of a lively Maggot, and 

 most commonly in a few Minutes afterwards puts out 

 its Wheels, and swims vigorously through the Water in 

 Search of Food : or else, lixing bv its Tail, works them 



Fig. 2.— a tardigr.\de, showing internal org.\ns. 



in such a Manner as to bring its Food to it. But 

 sometimes it will remain a long While in the Maggot 

 Form and not shew its Wheels at all." 

 Still another group of animals very wideh" distributed 



are the threadworms or Nem.^todes. Some of these 

 live freely in the earth or water, but a great number 

 of them are parasitic or live inside the bodies of other 

 animals or plants. Amongst the parasites of the 

 latter is the threadworm which causes the ear-cockles 

 in corn. These cockles are brown or purple galls or 

 tumours which replace the grain of corn and each 

 of which contains hundreds of minute microscopic 

 thread-worms. Motionless and apparently dead, but 

 not deca\'ed, in these galls the little worm can live in 

 dr3-ness for at least twenty years. But when moistened, 

 and this usually takes place by the gall falling on 

 damp ground, they resume their activities, making 

 their way to the young wheat plants and, wriggling 

 up the leaves and stems, find their way again to the 

 ear. Here thej^ pair -and laj^ numerous eggs from 

 which the threadworms of the ear-cockle arise. 



Snails and Slugs 



It should be noted that, whereas in the case of the 

 rotifers or the tardigrades the animal shrivels and 

 loses its outline, this is not the case with the thread- 



FlG. 3.— A TARDIGRADE, DRIED, IX \ ST.\TE OF 

 APPARENT DEATH. 



worm, and the suspended animation is prolonged and 

 not seasonal. But many other animals in the temperate 

 zones go into retreat during the winter, whilst in 

 warmer climates they hide away during the hotter 

 months of the 3'ear, or perhaps one had better say 

 during the diy season. For instance, many snails 

 hibernate during the winter. Most land-snails, as 

 the first frost nips the vegetation, retreat under stones 

 or into cracks or crannies in walls in tree trunks. 

 Others bury themselves deep in the earth or under 

 moss and leaves. Many common snails are often found 

 living together in clusters, in some sheltered retreat, 

 or, rather, not so much living as surviving. On the 

 other hand, slugs usually hibernate alone. They 

 excavate a nest in the earth, contract until they become 

 almost spherical, and lie in their retreat in a hardened 

 slime. The snails close their shells by the secretion 

 of a membrane or chalky valve, and both snails and 

 slugs take care to be in good condition before beginning 

 their winter sleep. And for this reason our Allies who 

 eat snails usually prefer those taken during the autumn. 

 During this hibernation their breathing and circulation 

 are reduced to a minimum and during the winter they 

 lose weight. 



