V A GLIMPSE INTO THE PAST 135 



passed through the tropics to reach the temperate 

 countries in the far south. For the origin of 

 these temperate forms in southern Australia we 

 are forced to look for a land connexion elsewhere, 

 and the close affinity which so many of these forms 

 show to the inhabitants of temperate South America 

 points strongly to a connexion through a sunken 

 Antarctic continent. We may now examine a 

 few of the groups of animals which especially 

 point to this connexion. Although the fresh- 

 water Crustacea are not very commonly employed 

 to illustrate an argument on geographical distri- 

 bution, it so happens that they are very instruc- 

 tive in regard to this particular problem. The 

 Crayfishes of the southern hemisphere form a 

 family (Parastacidae) quite distinct from those of 

 the northern hemisphere (Astacidae), differing in 

 several points, the most striking perhaps being 

 the entire absence of appendages on the first 

 abdominal segment of the male in the southern 

 forms. These southern Crayfishes inhabit tem- 

 perate Australia, New Zealand, Madagascar and 

 South America. Although a few species, especially 

 in South America, range northwards into the 

 tropics, the group as a whole is characteristic of 

 the temperate regions of the southern hemi- 

 sphere. 



In southern Australia and Tasmania the streams, 

 especially the mountain streams and tarns at a 

 great elevation, swarm with numerous species of 

 Amphipods, closely allied to the English fresh- 



