154 JUNE. 



dual transfer of the water, the habits of the animals 

 have also changed gradually, and that without any out- 

 ward alteration of form. Professor Loven thinks that 

 there is sufficient evidence to show that this change in 

 the condition of these lakes must have taken place 

 during the great glacier period, at a time when the 

 animals now found in it (and which are known at this 

 day only to inhabit the extreme north) could have lived 

 in the same latitude as the south of Sweden. The evi- 

 dence of these fresh-water lakes suggests that similar 

 changes in the relative position of sea and land may 

 have been the cause of our having fresh-water Crusta- 

 cea nearly allied to marine species in our rivers and 

 inland streams. 1 



Crawling about perpendicular faces of rocks, generally 

 at a considerable distance above high-water mark, we 

 may find a crustacean, not very remotely allied to these, 

 of rather large size. 2 It is broad and flat, a form which 

 marks it as belonging to another order, though in many 

 peculiarities of structure agreeing with its near neigh- 

 bours the high-backed Screws. The present species 

 crawls readily with its fourteen short strongly-hooked 

 feet, with which it clings to every little roughness of the 

 stone. It swims much less effectively : indeed, I have 



1 Bate and Westwood, p. 391. 



2 It is named Ligia oceanica, and is represented in Plate xvn., in the 

 centre of the picture. 



