3SO DISCOVERY REPORTS 



Arctic in one direction, and southwards to the Antarctic, along the west coast of Africa, 

 in the other, with a lateral path of migration extending into the Indian Ocean. The 

 remaining sections of the Desmacidonidae, the Myxilleae and Clathrieae, are world- 

 wide in distribution ; but here again the more primitive species are found in the North 

 Atlantic, and so far as the Myxilleae are concerned, the more highly developed species 

 are found in the sub-Antarctic and Antarctic. 



Nor can we ignore the coincidence that the widely distributed and primitive species 

 lophon proxhmmi, Tedania nigrescens and Amphilectiis fiicoriim, with a very variable 

 spiculation or external form, have a number of more highly developed species, which 

 appear to have developed from them, around the fringes of their areas of distribution. 



With the line of progression from Europe to the Antarctic, down the west coast of 

 Africa, shown by the species oi Isodictya, Amphilectiis, Mycale, lophon and Tedania, may 

 possibly be correlated the curious, discontinuous distribution shown by the species of 

 Plakina (P. monolopha, P. dilopha, and P. trilopha, together with several others) which 

 are found only in the Mediterranean and the Antarctic. The full significance of this 

 cannot yet be assessed, but it is a matter which should not be overlooked. How this 

 particular distribution has been efi'ected is a question which raises numerous difficulties. 



Br0ndsted (1926) has suggested that the distribution of New Zealand sponges may be 

 best explained on the Wegener hypothesis ; but whereas, in some parts of the world, the 

 Wegener hypothesis will explain the distribution of sponges as well as any other hypo- 

 thesis yet put forward, it is entirely insufficient in dealing with the sponges of the Atlantic 

 Ocean. The main features of the distribution of sponges in this area are on the whole 

 contrary to what might be expected on the Wegener hypothesis. They are as follows: 



(i) The dissimilarity of the fauna of the eastern coast of the United States of 

 America and that of Europe. 



(2) The similarity between the fauna of the West Indies and that of the Indo- 

 Australian area. 



(3) The existence of species common to the European and West African coasts, 

 the sub-Antarctic (as represented by the Falkland Islands area) and the Antarctic, and 

 their absence elsewhere in the Atlantic. 



(4) The presence in the Antarctic of several species found hitherto only in the 

 Mediterranean. 



Nor can the "creeping" of species around the coasts explain more than a small 

 proportion of the facts of distribution of species. I have already suggested (1930) a 

 correlation between the main surface currents of the ocean and the distribution of 

 sponges in the North Atlantic, and it is now proposed to show that a similar correlation 

 exists in the South Atlantic and Indian Oceans. 



