AMPIIirODA AND ISOPODA OF THE FIRTH OF CLYDE. 59 



are sometimes met with in the hollows of the alga, 

 Leathesia tuber i for mis, and in the air-vessels of 

 Fucus nodosus. In almost every ease where the 

 air-vessel was perforated it contained one of this 

 species, and sometimes tw T o, as above mentioned. 

 The perforations in the air-vessel were generally 

 irregular, both in form and size, frequently so large 

 as to let in the point of the little linger, and often 

 extended through both sides of the vessel. Those 

 containing the amphipod were filled more or less 

 with a soft leathery substance under which the 

 animal was concealed. It did not appear that the 

 amphipod had perforated the hole, as it was irregular, 

 and much larger than was required for the animal 

 to get in and out by, and therefore more exposed 

 to the attacks of its enemies. These air-vessels are 

 also occupied by a hydrozoon, but whether it can 

 be credited with the cutting of the opening I 

 cannot say. As I have not, however, observed such 

 lacerations on any other portion of the plant, it 

 may be inferred that the air-vessel has some 

 attractions for the depredators, whatever they 

 may be. 



As the Fucus nodosus is found plentifully about 

 half-tide, the anrphipod must often in w r et weather 

 be exposed to the fresh -water which then fills its 

 -cell. To test how long the animal could live in 

 that element, one w r as placed in a cupful of rain- 

 water, where it sank to the bottom as if dead. 

 About a minute later, when touched, it swam 

 round the dish with much vigour for a short time, 

 and afterwards settled on its feet for a little, 

 where it remained motionless, the antennae stand- 

 ing out and forming a kind of square. In 16 minutes 

 it turned over on its back, the movements of the 

 natatory legs becoming less regular, and stopping 

 at short intervals for a second or two. In 10 

 minutes more they became more rapidly worked, 

 the claws widely opened, and some of the posterior 

 legs twitched a little. At 30 minutes they stopped 



