6 NOTES AND COMMENTS [july 



Bryozoa and Bipolarity. 



Sir John Murray may take heart again. His attempt to explain 

 the similarity between the north and south temperate faunas has 

 been met by more that one specialist (even among those quoted in 

 support of his argument) by a denial of the similarity, at all events 

 to the extent assumed by the bipolar hypothesis. But now comes 

 a lady to defend the knight. Miss Edith M. Pratt, of Owens 

 College, Manchester, has been studying some collections, chiefly of 

 Bryozoa, made on the shore of the Falkland Islands {Manchester 

 Memoirs, vol. xlii. No. 13, 14th December, 1898). After a careful 

 analysis of the distribution of the genera, she concludes that the 

 results " as far as Bryozoa are concerned, seem to support Murray's 

 theory." " Each genus represented in the collection occurs fossil, and 

 also occurs in the north and south temperate zones, as well as in the 

 tropics ; in fact most of the genera are cosmopolitan. Many of the 

 species are represented in the Tertiary deposits. This shows that the 

 changes of climate and the altered conditions of life have not affected 

 their ' Tertiary ' structure ; as many of these forms occur only in the two 

 temperate zones, there is reason to believe that they have retained 

 their common ancestral structure. The fact of many of the species 

 occurring in the deep sea hardly supports Ortmann's theory [that an 

 exchange of polar forms can take place through the deep sea], for 

 many of them occur at very great depths only in the temperate 

 regions ; in the tropics they occur in shalloiv water. Their presence in 

 the deep sea is, I think, the result of accident." 



It is pleasing to find some attention paid to distribution in former 

 geological periods; but does Miss Pratt, or can Sir John Murray, 

 suppose that what took place in Tertiary times has much bearing on 

 the question ? It cannot seriously be maintained that there was any 

 appreciable difference of world-temperature so recently as the Tertiary ; 

 certainly there was no approach to a universal climate in those days. 

 We have to go back a good deal farther before our facts can bear any 

 relation to the primal temperature of the globe. If there be a 

 similarity between the present polar faunas, we do not see how any 

 identity of species can be due to events that took place, if at all, 

 in early Palaeozoic ages. As for certain cases of distribution being 

 " the result of accident," what can Miss Pratt mean ? It is too easy a 

 way of explaining inconvenient facts. 



Miss Pratt also studies the distribution of Anthomedusae, Porifera, 

 Polychaeta, Gephyrea, Mollusca, Echinoderma, Crustacea, and Tunicata. 

 Out of twenty-four species, three have been recorded from north and 

 south temperate regions only ; one from north and south temperate 

 regions and the tropics ; one from tropics and southern hemisphere ; 

 and all the rest from the southern hemisphere only. These facts 

 scarcely show a striking similarity between the temperate faunas of the 



