ZOOLOGY : MARINE INVERTEBRATES. 87 



readily in their native habitat where, in the shadow of the cas- 

 tellated cliffs, they seem not to be affected by the drawing off of 

 most of the water, but remain with tentacles spread and bodies 

 fully expanded, to the delight of the observer. When the water 

 is warmed by the sun, the animals contract. This species is quite 

 hardy, and can be kept in an aquarium for weeks, provided the 

 water is kept cool and is changed every few days. It may be fed 

 on bits of meat, snails, etc. 



The frondose bryozoan Bug id a turrita occurs abundantly in 

 these tide-pools, and can be distinguished readily from the hydroids 

 associated with it, by the flat character of its branches. This spe- 

 cies shows the avicularia well ; and under the microscope these 

 may be seen active in a living specimen, if kept in salt water. Mem- 

 branipora pilosa and other species of encrusting bryozoans are 

 found on the branches of the rockweed, as well as the Chondrus 

 crispus; and with these on the latter alga, may be found commonly 

 the spiral shell of the sedentary worm Spirorbis borealis. Hydroids 

 are abundant, but they are mainly campanularians. Campanularia 

 flexuosa is not an uncommon species on the rocky walls of the tide- 

 pools, but is more frequent under the rockweed about the rims 

 of the pools. Sertularia pumila, most at home on the rockweed, 

 nevertheless occurs in the pools, although much less commonly than 

 on the rockweed. The two delicate species of campanulate hy- 

 droids, Clytia bicopkora&ndC. (Orthopyxis) poterium, are also com- 

 mon in these pools ; and with them occur numerous other animals, 

 which are found likewise in the tide-pools of East point. 



EAST POINT, SAHANT. 



Route. — From Lynn by barge or bicycle, across Nahant neck to 

 the Lodge estate. Follow foot-path to cliff. 



At East point, Nahant, the cliffs are composed of metamorphosed 

 slates and limestones with several intrusive beds (see pp. 10-18), 

 the whole dipping inland at a high and practically uniform angle. 

 Owing to' the varying hardness of the beds, and the erosion of 

 the softer in preference to the harder, a number of more or less 

 completely enclosed tide-pools are formed at various levels, all 

 of them containing an abundance and variety of marine organ- 

 isms. The best of these are in the vicinity of Pulpit rock, and 

 are accessible at low water. The margins of these crystal pools 



