152 SEA-SHORE LIFE 
however, not derived from the plumed gills of other snails, but are 
a new formation found only among the Nudibranchiata. The back 
is apt to be covered with finger-shaped processes which proba- 
bly function in respiration, and the head is provided with eyes 
and tentacles. 
These most interesting little snails match their surroundings 
to a wonderful degree of perfection, their ragged-looking backs and 
mottled color giving the impression of a piece of torn seaweed. 
They crawl upon sea weeds or stones, but can also swim foot up- 
wards along the surface of the sea. 
Holis papillosa is the commonest species under stones or upon 
sea weeds in shallow water off our north Atlantic coast, and the 
shores of Europe. It grows to be about three inches long, but spe- 
cimens over an inch in length are rare. It is very variable in 
color, being fawn, gray, or yellowish sprinkled with large dots of 
white, olive, brown, purple or yellow. The body is square in front 
but tapers to a point behind. There are two pairs of tentacles 
upon the head, and numerous rows of papille, down both sides, the 
middle of the back being bare. The eggs are laid in a white gela- 
tinous cord, festooned and coiled in a spiral, and deposited upon 
stones. A good figure and description of this creature is given by 
Gould and Binney. ‘Invertebrates of Massachusetts,” p. 238. 
Plate XVIII. Figs. 257-263. Curiously enough the skin of this 
creature is provided with stinging thread-cells similar to those of 
jelly-fishes and sea anemones. It is probable, however, that these 
thread cells may have been obtained from sea anemones upon which 
the mollusk has fed. 
Ancula sulphurea is a pale yellow species commonly found on 
rocky bottoms off the New England coast north of Cape Cod; being 
very abundant in water about 200 feet deep. 
THE SQULD; OCTOPUS ANDO NAUTILUS, 
Cephalopoda. 
These are the most highly developed mollusks, and when one 
observes their remarkably rapid movements, their acute senses, and 
the complexity of their entire organization, it is difficult to convince 
one’s self that their nearest Jiving relatives are snails and clams. 
They are all carniverous, and prey upon fishes, crustacea and 
other mollusks which they capture by darting backward, seizing 
