6 
INTRODUCTION. 
patched with Cynthia grossularia either singly or in groups, 
each with its brick-red tunic and prominent papillae. A 
miniature forest of Sertularia pumila is carpeted by pinkish 
Lepralia s and gelatinous molluscoids of diverse patterns and 
colours. White Serpulce and the sandy tubes of Sabellaria 
are mingled with the coils of hosts of Spirorbis. Sponges of 
various species, developing Medusce , molluscoids, nudibranchs, 
and other mollusks, starfishes and their ova, annelids and 
crustaceans, reward a careful search. Some shallow pools, 
again, are hollowed out of the surface of the bare rocks near 
high-water mark, e. g. near the Maiden rock; and in each of 
these dwell a group of Littorina rudis , numerous sessile-eyed 
crustaceans, a solitary anemone (A. mesembryanthemum) and 
a few limpets, the latter bearing the most conspicuous vegeta¬ 
tion on their shells. 
Certain pools, especially near the pier, begin by a shallow 
margin, but end deeply against a perpendicular wall of rock, 
the bottom thus gradually shelving downwards. On the shal¬ 
low border Ceramium rubrum and other seaweeds tuft the 
slopes, and are the favourite cover of many specimens of Ca- 
prella tuberculata , whose red bodies can scarcely be recognized 
amongst the branches. Each plant of Ceramium rubrum , 
indeed, is the abode of a marine colony. Hippolytae cling 
to the boughs, their translucent bodies forming excellent 
subjects for the microscope, even where colour and outline are 
the only objects; they exhibit lively motions of the antennae, 
maxillipedes, and the ambulatory limbs; while internally the 
flattened branchial and other whips vibrate with rapidity. 
Idotea tricuspidata darts from place to place, climbs up the 
branches, or remains stationary on a twig. Small sessile-eyed 
crustaceans alternately swim through the water, and run like 
monkeys along the boughs. Many little mussels with hairy 
valves hang motionless as fruit on the branches. Rissoce 
move up and down the twigs—stretching their delicate white 
tentacula and blunt snouts, or vary their exercise by floating 
on the surface, shell downwards. Some detach themselves 
and pass swiftly to the side of the vessel and out of the water, 
thus forming a voluntary and sometimes useful segregation. 
Lacunce also occur on the branches, and twist their muscular 
