2go 



SCIENCE-GOSSIP. 



nucleus is embedded. Similar in appearance, only 

 smaller, are the white blood and lymph corpuscles 

 of the vertebrates. Protoplasm, then, represents 

 the essentially active element of the cell, and its 

 properties are consequently the attributes of life, 

 and can therefore be rapidly distributed ; it 

 possesses the power of absorbing or secreting 

 oxygen — the pubulum vita?, — and in exchange giving 

 off carbonic acid ; it is also the seat of a kind of 

 true pulsation. In the activity of eliminating 

 the carbonic acid gas, other substances or waste 



products are given off in company, and, naturally, 

 new elements are introduced into the mass and 

 absorbed, setting up the process of nutrition. If the 

 elements so introduced are in excess of those dis- 

 charged we have the phenomenon of growth ; but if, 

 on the contrary, the elements given off are in excess 

 of those introduced or absorbed, we have diminution 

 in proportion as the excess is smaller or greater, 

 and which, if carried on in continuity, results in 

 dissolution — that is, the death of the organism. 

 (To be continued.) 



COLORATION AND VARIATION OF BRITISH 



EXTRA-MARINE MOLLUSCA. 



By Arthur E. Boycott. 



{Continued fr 



T T has been said that mollusca have to contend 

 against many animal enemies in the sea ; they 

 have also to withstand that physical agent, the 

 wave-wash, which is constantly striving to batter 

 them in pieces. A. R. Hunt (*) has made some 

 most interesting observations on this subject, and 

 has shown how species with a strong development 

 of the lip, or of sculpture in the form of spines, 

 thus gain a broad base for a sandy bottom, which 

 helps them to resist their special danger, viz., the 

 alternate swing of waves on the bottom. Experi- 

 mentally, in a tank, it appears that such species as 

 Murex monodon (Australia), Aporrhais pes-pelicani 

 (Torbay), Stromhis tricomis (Red Sea), etc., while 

 very hard to overturn by wave-effects from their 

 natural attitude of rest with the mouth downwards, 

 are, when once upset, very easily turned right 

 again by the alternate swinging of the water at its 

 bottom in shallow depths. Even in comparatively 

 deep water (fifteen to forty-one fathoms) shells 

 may be damaged considerably ; a specimen of 

 Trochus granulattis from Torbay, in fifteen fathoms, 

 had repaired breakages nine times, and of a 

 miscellaneous parcel of shells from the Channel 

 fishing-grounds, sixty-eight per cent, showed signs 

 of damage caused by some agent external to them- 

 selves. This inimical wave-wash accounts at once 

 for one of the two striking characteristics in which 

 marine differ from freshwater mollusca. The 

 thickness and solidity which is so striking in most 

 sea shells, prevents, or tends to prevent, fracture 

 on being dashed about among stones and rocks by 

 the waves. 



It seems then that marine mollusca lead a hard 

 life ; but when we come to our quiet ('-) streams and 



(1) " On the Formation of Ripplemark," Proc. Roy. Soc, 

 xxxiv. (1882), p. 1. 



( a ) J. Madison (Journ. Conch., v. p. 2G1) thinks that the 

 shape, strength, etc., of Limnaea peregra var. burnetii saves 

 it trom being broken when the stones on which it sits 

 are rolled about by the waves. 



om page 258.) 



ponds, we find a very different state of things. 

 The population is more scanty, at any rate as lar 

 as large predacious animals are concerned, and 

 the shells of the characteristic genera are thin 

 and monochromatic. Charles Darwin long ago 

 remarked on the fact that competition was and 

 has been less severe in fresh water ( s ). The cod 

 and other large fish are replaced chiefly by the 

 trout, roach, etc., which chiefly affect localities 

 where Limnaea is not so numerous as in the ponds 

 they chiefly inhabit, where the fish are not numerous. 

 Roach are reputed to eat snails' eggs ( 4 ) ; and 

 there is no doubt that trout feed readily on snails. 

 L. peregra var. burnetii was first taken in a trout's 

 stomach in Loch Skene, Dumfriesshire ("»), and has 

 been found by Walker in a similar situation in 

 the Gillaroo trout (Salmo stomachicus), in a lake in 

 Co. Tipperary ( c ). W. Jeffery has recorded finding 

 about 350 shells in the stomach of a large eel, 

 in Sussex, principally Valvata piscinalis, but also 

 Planorbis complanatits and Bithinia tentaculata. Mr. 

 H. C. Moore tells me that he has frequently 

 found shells in the stomachs of trout caught 

 in the Aymestrey waters of the Lugg, in the 

 north of Herefordshire, and has shown me 

 several Limnaea peregra thus procured. He was good 

 enough to collect for me in the end of May last 

 year (1896) all the shells from the stomachs of 

 twelve trout from the locality mentioned. They 

 consisted of Valvata piscinalis, thirty-three; Ancyius 



(3) '1 Descent," ed. vi. p. 83. 



C) F. Buckland, " Curiosities of Natural History," i. (1890), 

 P- 255. 



( 5 ) E. Forbes and S. Hanley, Hist. Brit. Moll., iv. (1853), 

 p. 173. 



(6) J. G. Jeffreys, B. C. v. (18C9), Suppl., p. 153. H. G. 

 Seeley considers that the muscular thickenings 01 the walls 

 of the stomach, characteristic of this species ("local race"), 

 have arisen from its diet of Limnaea, Ancyius, etc. " Fresh- 

 water Fishes of Kutope" (1886), p. 280. K. Collier has 

 recently recorded Limnaea peregra-lacitstris and Pisidium 

 pusillnni from a trout's stomach from an Irish lough. 

 J. C, viii. (1897), p. 331. 



