54 PRIMITIVE ANIMALS 



mountains in Tasmania. Nor have we any clue as to 

 why this animal has disappeared from the sea and 

 survives only in the fresh- waters of one small corner 

 of the world, while the still more ancient Nebalia, as 

 far as we know, has never penetrated into fresh-water 

 nor suffered any diminution or restriction of its range 

 in the sea. 



The interest of Anaspides, besides its great 

 antiquity and geographical isolation, is that it serves 

 to connect the various groups of the higher Crustacea, 

 the Malacostraca, with one another, and the study of 

 its anatomy has done a great deal to show that the 

 old classification of the higher Crustacea was erron- 

 eous, and to point out the true lines of cleavage. The 

 older systematists drew a fundamental distinction 

 between Malacostraca with a carapace and stalked 

 eyes such as the Shrimps, Crayfish, and Crabs, and 

 those without a carapace and with sessile-eyes, viz. the 

 Isopods and Amphipods. Anaspides possesses stalked 

 eyes but it is without a carapace, as its name implies ; 

 and in the rest of its characters it shows the same 

 eclecticism, resembling in some features the more 

 highly organized stalk-eyed forms and in others the 

 sessile-eyed group. It is evident, therefore, that the 

 structure of the eyes and the presence or absence of 

 a carapace cannot be used as classificatory characters 

 of the highest importance. This is borne out by the 

 fact that certain marine shrimps, the Mysidae, which 



