[317] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 23 
terior legs, and extending the body out at an angle, with-the long, rough 
front legs stretched out in various directions. While in these attitudes 
and at rest they often closely resemble the branches of the hydroids 
and alg among which they live, especially as they also imitate them in 
colors, for all these species are variable in color, being generally gray, 
with darker specks, when living among hydroids, but often bright.red 
when living among red alge. This habit of holding themselves stiffly 
in such peculiar positions recalls the similar habits of many insects, es- 
pecially some of the Orthoptera and the larvee of the geometrid moths, 
and they also recall the larve, just named, by their singular mode of 
climbing actively about among the branches of the hydroids and alge, 
for they bend the slender body into a loop, bring the hind legs up to the 
front ones, and taking hold with them stretch the body forward again, 
just like those larve, though their legs are long and slender and differ 
widely in structure. These little creatures are very pugnacious and are 
always ready to fight each other when they meet, or to repel any in- 
trader similar in size to themselves. Their large claws are well adapted 
for such purposes. 
. The marine worms or Apnelids are very numerous under the rocks be- 
tween tides, and concealed beneath the surface of the gravel and mud 
, that accumulates between and beneath the stones and in crevices. 
Many kinds also live in the pools, lurking among the roots of the alge, 
burrowing in the bottom, or building tubes of their own in more ex- 
posed situations. Many of these annelids are very beautiful in form 
and brilliant in color when living, while most of them have curious hab- 
its and marvelous structures. Several species are of large size, grow- 
ing to the length of one or two feet. Some are carnivorous, devouring 
other worms and any other small creatures that they can kill by their pow- 
erful weapons; others are vegetarians; but many are mud-eaters, swal- 
lowing the mud and fine sand in great quantities, for the sake of the 
animal and vegetable organisms that always exist in it, as is the case 
with clams and most of the bivalve shells, and many other kinds of 
marine animals. 
All these Annelids are greedily devoured by most kinds of marine fishes, 
whenever they can get at them, and, since many of the annelids leave 
their burrows in the night to swim at the surface, or do this constantly 
at the breeding season, they make an important element in the diet of 
many fishes besides those that constantly root for them in the mud and 
gravel, like the tautog, scup, haddock, &c. The young of nearly all 
the annelids also swim free in the water for a considerable time, and 
in this state are doubtless devoured in immense numbers by all sorts of 
young and small fishes. 
. One of the largest and most common Annelids found under rocks, 
burrowing in the sand and gravel, is the Nereis virens, (Plate XI, figs. 
47-50.) It lives both at low-water mark and at a considerable distance 
farther up. It grows to the length of eighteen inches or more, and is 
