766 



THE NATURE BOOK 



The tadpoles of the common Frog are 

 also to be found in the ponds, and their 

 gradual development is a most interest- 

 ing and remarkable sight. 



Every pond will be found to include 

 amongst its inhabitants a number of 

 shell-dwellers, the different species of 

 Water Snails and Fresh-water Mussels. 

 Though when collecting pond life one is 

 apt to pass these creatures unheeded, 

 they should not be neglected, for a little 

 closer examination will show them to 

 be very remarkable and interesting, 

 and many of them display considerable 

 beauty of colour and form. 



Of all the pond snails, probably the 

 one most frequently to be met with is 

 Limncra stagnalis. The shell of this 

 snail is thin, horny, and ovately turreted, 

 with an elongated and sharply pointed 

 spire. It is a handsome creature, and 

 fairly active. It crawls about amongst 

 the submerged weeds, and when un- 

 disturbed, with its body fully protruded 

 from its shell, will be seen to have a 

 broad, short head, and somewhat flattened 

 tentacles, near the inner base of which 

 the eyes are placed. This snail may 

 frequently be seen gliding along beneath 

 the surface of the water, shell downwards, 

 and if alarmed it will at once sink to 

 the bottom of the pond. The Limncea 

 deposits its spawn in oblong, transparent 

 masses on water plants and stones. 

 With the approach of severe cold it 

 becomes lethargic and hibernates in the 

 mud at the bottom of the pond. 



Limncea anricularia, although not so 

 common as Limncea stagnalis, is by no 

 means rare ; while it has a much smaller 

 shell, the body-whorl is larger than that 

 of stagnalis, and has the outer lip reflected. 



The most abundant of our native species 

 of Limnceidce is the Limncea peregar. It 

 is a most extraordinarily prolific creature : 

 Dr. Gwyn Jeffreys states that it lays 

 about thirteen hundred eggs in numerous 

 clusters. It is very active in its move- 

 ments, and is given to creeping up the 

 stems of the aquatic plants and remaining 

 for some time out of the water. 



Planorbis is another water snail com- 

 monly found in ponds. It is a creature 

 with a very wide distribution, species 

 being found throughout Europe, >s"orth 

 America, India, and China. In all there 



are some 145 species in existence, while 

 about sixty-nine fossil species have been 

 found in the W'ealden formation, in 

 company with some seventy species of 

 the Limnceidce, which shows that these 

 pond snails are a very ancient race of 

 creatures. Planorbis has a character- 

 istic habit when crawling along, of 

 trailing its shell behind its half-extended 

 body. 



Palndina vivipara also comes of an 

 ancient stock, the fossil remains of its 

 ancestors contributing largely to the 

 composition of the marbles of the Wealden 

 and Purbeck beds. It is a pretty active 

 snail, and has a rather handsome shell, 

 ornamented with coloured bands. A near 

 relation of Palndina, called Bvthinia, is 

 much smaller, and appears to be of a 

 more social disposition, as it may gen- 

 erally be found in considerable numbers. 

 While Palndina is viviparous, that is to 

 say, generally brings forth its young 

 alive, Bythinia is oviparous, laying from 

 thirty to seventy eggs in a band of three 

 rows on stones or pond plants. The 

 young hatch in about three to four weeks, 

 and take two years to attain their full 

 growth. 



The River Mussel [Unio Margadiferns), 

 to be found in ponds fed by streams, is 

 particularly interesting from the fact 

 that it is the species that provided the 

 once famous British pearls. The Scotch 

 pearl fishing was at one time an industry 

 that yielded a profitable harvest, and 

 the pearls were usually found in old and 

 somewhat deformed specimens of mussels ; 

 round and perfect pearls about the size of 

 a pea were worth from ^^^3 to £4. 



Sir R. Redding, in the " Philosophical 

 Transactions, i6q3," gave an account of 

 the Irish pearl-fishing, in which he states 

 that the mussels were found set up in 

 the sands of the river beds with tlieir 

 open side turned from the torrent, that 

 about one in a hundred might contain a 

 pearl, and that about one pearl in a hun- 

 dred might be tolerably clear. It is not 

 very surprising that with sucli a ]-)oor 

 yield the industry has become practically 

 extinct in both countries. 



Anodonta, the Swan-mussel, is the largest 

 of our pond and river mollusca, and is a 

 very handsome and interesting creature. 

 When undisturbed it may be seen with 



