SOME OTHER CRUSTACEA. 217 



differs in the compressed shape, and in the fact that the 

 thoracic appendages bear breathing organs, while the 

 abdominal are used for swimming and jumping. As special 

 characters are to be noticed the absence of the anterior 

 antennae (antennules), and the great length of the posterior. 

 Of the seven thoracic legs the first pair are larger than the 

 second. The first three abdominal appendages are turned 

 forwards, and are used for swimming; the last three are 

 turned backwards, and are used for jumping. The colour, 

 as everyone knows, is a peculiarly glassy yellowish white, or 

 occasionally a dark dirty tint. 



Under stones in the rock pools the true sand-hopper is 

 replaced by swarms of another little creature of similar size. 

 This is Gammarus locusta (see 

 Fig. 63), the great scavenger of 

 the rock pools, as the sand- 

 hopper is of the shore. It 

 is easily distinguished from the 

 latter by the fact that the an- 

 terior antenna (antennules) are 

 well developed, and have two 

 filaments each. When suddenly 

 uncovered by the removal of the 



Stone Under which it has been FIG. 63. Gammarus locusta. Note 

 i /-v i ! , the two pairs of feelers and the 



lying, GammarUS exhibits a number of legs, of which there 



curious sidelong movement, which J en pairs belon g in g to the 

 seems to combine the maximum 



effort with the minimum result. If you shake out a bunch 

 of weed in water, however, you will find that the little 

 animals can swim swiftly enough. 



Another somewhat interesting shore Amphipod is Amphi- 

 thoe podoceroides, which makes nests of weeds under stones. 

 The nests are often of considerable length, and very neatly 

 woven, and are a source of much disappointment to many a 

 young shore naturalist. The nest is found with joy, and 

 torn open by careful fingers, eagerly expectant of a prize, 

 when instead out shoots the Amphithoe, or oftener, perhaps, 

 two of them, male and female together. Why they should 

 be a disappointment perhaps is not obvious, but it is an un- 

 doubted fact that most people cannot carry their enthusiasm 

 as far as Amphipods. The species named reaches a length 



