NERKIS. 161 
devised. Science would be thence greatly benefited. Travellers shun the 
path beset with asperities. 
I doubt not that merely viewing the precise configuration of the 
two extremities, would very much lead to a suitable distribution of this 
curious tribe, to which should be added the more conspicuous appendages. 
At least the characters found in all these, would preserve the practical 
naturalist from resorting to the destruction of a living creature for the 
sake of satisfying his curiosity in searching for hidden organs. 
In the pursuit of knowledge, the cause of humanity should never 
be forgot. 
But the arrangement of the genus in detail is embarrassing, and 
particularly from the ignorance of the observer, as to whether his sub- 
ject is entire. Next is the great variety of species, and the searcity of 
some, which prevents the naturalist from corroborating previous obser- 
vations. 
From these causes, naturalists are compelled to limit their scope of 
a subject otherwise sufficiently comprehensive. 
In general these animals prefer a sandy site ; they dwell in conceal- 
ment ; nor do they court the light, or voluntarily expose themselves to 
view. All have the faculty of protecting themselves, either by a copious 
elutinous secretion from the body lubricating its parts, constructing a 
simple sheath of silky matter, or by a covering compounded of such 
matter with earthy particles or sand. There they lurk im safety, com- 
monly below, but some establish themselves on the sides of vessels at some 
distance from the bottom. The natural secretions are extraordinarily 
copious in some. The artificial covering leaves the head exposed, which 
is seen waving continually from side to side. 
Among the members of this numerous tribe, are found the finest 
illustrations of the luminous properties recognised among the lower ani- 
mals, in the Nereis noctiluca, a diminutive species, not exceeding the 
length of half an inch. When transferred amidst a quantity of marine 
collections to a glass jar, it commonly ascends to the very edge of the 
water, and there secures itself just under the surface, in a silken sheath 
applied to the side of the vessel, reposing almost continually in the spot 
x 
