ANTARCTIC SPECIES OF TEDANIA 



347 



The picture presented by the distribution of these species (Figs. 44, 45) is thus a 

 very interesting one. We have one species, T. nigrescem (Schmidt), the least speciaHzed 

 of the genus, variable in form, having a wide distribution, and all round the margins 

 of its area of distribution are found species of slightly more advanced development 

 and greatly restricted distribution. The culmination is found in the sub-Antarctic 

 and Antarctic species which appear to show a continued progression in development 



Fig. 45. Plan of distribution of the species of loplwii. Tlie shaded area represents the distribution of 

 /. proximum, Ridley, the darker lines coinciding with localities at which the species has been actually recorded, 

 the thin lines where it may be assumed to occur. The size of the black dots, representing the remaining 

 species of the genus, are proportionate in size to the degree of specialization of the species. 



as the Antarctic is approached, until, within the Antarctic itself, we have the three 

 most specialized species of all, T. charcoti, T. massa and T. oxeata. This picture, in 

 fact, suggests the possibility that this variable species, fluctuating considerably in its 

 main characters, has given rise to a number of localized and more highly developed 

 species at various points ; and that from these have arisen other species with, generally, 

 an increasingly higher degree of specialization as the polar waters are approached. 



