6 INTRODUCTION. 



patched wit] i Cynthia gross ularia either singly or in groups, 

 each with its brick-red tunic and prominent papillae A 

 miniature forest of Sertularia pumila is carpeted by pinkish 

 Lrjiralia and gelatinous molluscoids of diverse patterns and 

 colours. White SerpuUv and the sandy tubes of SabeUaria 

 are mingled with the coils of hosts of Sjiimrbis. Sponges of 

 various species, developing Medusa;, 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. Hippolytce 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 antenna?, 

 maxillipcdes, 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. Riasoa 

 move up and down the twigs — stretching their delicate white 

 tentacula and blunt snouts, or vary their exercise by floating 

 op] 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. 

 Lacunas also occur on the branches, and twist their muscular 



