70 A NATURALIST IN TASMANIA ch. 



part of the body free, instead of being fused to 



form a shell or carapace, and the way that the 



body is held quite flat without any bend in it is 



very different from a shrimp or any of the other 



higher Crustacea. Moreover, all the legs are 



forked and consist of two branches, a character 



which usually occurs in the young stages of many 



of the Crustacea, but is lost to a great extent in 



adult life. Indeed, in all the chief points of its 



structure it shows a remarkable combination of 



characters, some of them being quite peculiar to 



itself, while others are taken, as it were, at random 



from all the chief groups of the higher Crustacea ; 



and this is what we should expect, on the principle 



of divergent evolution, a very ancient and primitive 



animal to do. One of its most interesting features 



is the double series of delicate leaf -like gills attached 



to the bases of the front limbs, which are kept in 



a continual gentle motion by the waving of the 



outer branches of the front legs, even when the 



animal itself is standing still. 



Curiously enough this creature resembles many 

 other of the Australian animals, e.g. the Platypus 

 and the Marsupials, in differing totally from all the 

 other members of its class in its method of repro-, 

 duction. In practically all Crustacea, and certainly 

 in the higher Crustacea generally, the female 

 carries about her eggs for a long period after 

 fertilization,' until they are ready to hatch out, 

 and for this purpose she employs either an elaborate 

 brood-pouch formed of imbricating plates which 



