Manchester Memoirs, Vol. xlv. (1901), No. 14. 5 



southern hemisphere. Yet, notwithstanding the changes 

 through which species have passed, we should expect to 

 find some forms, not very numerous perhaps, but still 

 some forms, which have remained more or less true to 

 their ancestral structure. Therefore, points of similarity 

 in extra-tropical forms, which are not shared with tropical 

 forms, have a m.ost important bearing upon the " Bipolar 

 Theory." It is but natural that the similarity would be 

 more marked in some groups than in others. 



It is to be greatly deplored that, owing to a want of 

 uniformity in the recognition of specific and even of 

 generic characters on the part of authors, many forms 

 have been regarded as new and distinct species or genera 

 which further investigation has shown should have been 

 included with previously described forms. Murray and 

 other writers have shown this to be a great obstacle in 

 the identification of many Challenger species. Therefore, 

 in order that the relationship between extra tropical forms 

 may be ascertained, it is imperative that, wherever possible, 

 an actual examination and comparison of these forms 

 with tropical representatives — -where they do occur — 

 should be made. 



In a paper supporting Ortmann's view in opposing 

 the theory, Professor D'Arcy Thompson ('97) states that 

 many of the forms included in Sir John Murray's list of 

 bipolar forms are recorded, not as identical, but as distinct 

 varieties, and maintains that this fact weakens the evidence 

 in support of that theory. 



It is admitted that the "Bipolar Theory" does not 

 necessarily depend upon tJie specific identity of bipolar 

 forms, but upon the relationship of these forms to each 

 other. Therefore, the fact that Arctic and Antarctic 

 specimens of the same species do show some constant 

 variation from one another strengthens the evidence in 



