NEPHTHYS. 171 



few minutes the agitation ceased, and they again lay motionless. I 

 now tried the effect of touching an individual with a small drop of 

 fresh water. The part to which the latter was applied almost im- 

 mediately contracted in the manner that a leech contracts at the place 

 where a little salt is applied to it, and then the whole animal became 

 agitated, and dashed violently about the plate, frequently, at the 

 same time, protruding and contracting its proboscis. Similar effects 

 followed every trial I made, and it mattered not what part of the 

 animal was touched : the smallest drop of water from the point of a 

 probe produced the partial contraction at the part, and then the 

 general convulsive writhing and agitation of the whole body. Even 

 fragments of the worm were similarly affected. It appeared to me, 

 however, that the mouth extremity was more sensible to the touch 

 of the poison than any other part, as the convulsive efforts which 

 followed seemed more violent and longer continued than when the 

 water was applied elsewhere. 



" I made similar trials on many of these animals, and invariably 

 found the same results. The most striking way of exemplifying the 

 virulent effects of fresh water is, when the worm is at rest, to apply 

 consecutively from the point of a probe ten or a dozen small drops 

 of sea water to any part of it ; this causes no alteration ; the animal 

 continues motionless. If we then change the drop to be applied from 

 salt to fresh, the very first application of the latter immediately pro- 

 duces the phsenomena above described. 



" In whatever way it is that fresh water proves so poisonous and 

 fatal to this species, one thing is obvious, that the animal can never 

 propagate except under the influence of sea water. It can never 

 colonize rivers or lakes ; and the subject, if further pursued by expe- 

 riments on other species, may, perhaps, throw some light on the 

 distribution of animals. The Lurg-worms cannot even safely inhabit 

 those parts of the shore which are long uncovered by the sea ; a heavy 

 shower of rain during ebb tide might destroy them ; and it is only a 

 casual circumstance that one of them is found in the usual place of 

 digging for bait. They must be sought for at the verge of low-water 

 mark, and they are only to be found in plenty, and of full growth, 

 during the neap tides. 



" The common Lug {Lumbricus marinus) is, on the contrary, 

 generally dug out of the sand at a considerable distance from low-tide 

 mark, and where it is left dry for many hours. Showers of rain, 

 therefore, we should suppose, can exercise no deleterious influence 

 on it ; and accordingly I found that some lug, which I kept immersed 

 for several hours in fresh water, did not seem to be at all incom- 

 moded by it." 



According to Quatrefages, the poisonous effect is chiefly owing to 

 the want of chloride of sodium (Rai/ Soc. Rep. Zool. 1847, 504). 



(«) Tenby, F. D. Dtjster. 



(b) Falmouth. 



(c) Berwick Bay, Dr. Johnston. 



(d) Berwick Bay, Dr. Johnston. 



((?) Littlehampton, Sussex, Miis. Leach. 



