412 Causes and Course of Organic Evolution 



While not denying a somewhat distant affinity in the main 

 phyhnn with such a series of marine types, the writer hopes 

 to show that a more condensed and mucli more direct continuity 

 can be traced at the present day, through small, simple, but 

 multicellular forms, intermediate between some of the ciliate 

 Infusoria and living forms of Rotifera, thence through primi- 

 tive and later through advanced members of the Turbellaria 

 to the fresh-water Nemertinea. From the last we hope to 

 show that the continuity is wonderfully perfect through a 

 semi-cyclostomatous to a proto-cyclostomatous fresh-water 

 ancestry. From the latter through a csecilian to a semi-uro- 

 dele type, the gradation is equally marked, while by some 

 fossil forms we seem to pass onward to a marsupial and later 

 to a high mammalian stage. 



We are fully aware that such a proposed plan upsets many 

 cherished classificatory tables of past years, but if the present 

 substitution is truly based on sound morphological principles 

 and on phylogenetic continuity it will doubtless be accepted. 

 If it is unable to stand the test of time, it can be set aside as 

 another earnest even if misdirected groping after the truth. 



But contrary to usually accepted views, and in line with 

 the evidence presented in the last chapter, we would emphasize 

 the statement that all of tliis evolution has probably — almost 

 certainly — proceeded, either in relatively shallow fresh-water 

 areas (using this designation in its widest sense) or even at 

 times on land, not in salt-water expanses and least of all in 

 ocean depths. Accordingly in speaking of some structural 

 details amongst the Rotifera, the Nemertinea, and the Cyclo- 

 stomata, that may now be best traced in brackish or marine 

 forms, we accept it that in not a few cases similar structures 

 may have been — probably even were — developed amongst 

 fresh-water or land species that may either be alive or are 

 now extinct. Our reasons for such a position are as follows: 

 while for example amongst the Nemertinea the fresh-water 

 and land types are now decidedly in the minority and do not 

 belong to the highest orders of the class, they are so evidently 

 and fundamentally in line with the higher marine forms, and 



