IGO Prof. yVI Irish's Notes from the 



■with sufficient continuity to evolve anvthing more than a 

 variation. 



The differences in the various races of Filograna do not 

 appear to be so great as to warrant specific separation, and 

 this is the more noteworthy in a species so widely distributed 

 and so plastic. The variations lead to no change of habit 

 or surroundings, no essential change in general structure, 

 and the diflFerent methods of reproduction remain more or 

 less the same throughout. No variety seems to excel the 

 other in its influence on the stability of the species, or to 

 lead to fixity and the formation of a new species, and the 

 " extermination of the older and less improved forms." 

 This species does not conform to the view that the " lesser 

 differences characteristic of varieties come to be augmented 

 into the greater differences characteristic of species " *. If 

 the struggle for existence held in the ordinary way, it is 

 reasonable to suppose that certain variations of structure 

 and development would have been singled out as permanent 

 — to the exclusion of others. 



The differences between the varieties of Filograna are 

 more pronounced, perhaps, than in such a case as A.. G. 

 Mayer's lipeuthesis folleata and Pseudoclytia pentatUy the 

 former with the typical four, and the latter with five radial 

 canals, gonads, and manubrial lobes. The Coelenterates, 

 moreover, have a more simple structure, and their gelatinous 

 tissues respond more easily to sudden variations. 



Whilst there is wide variability in the plastic branchiae, 

 eyes, opercula, the number of " thoracic " segments, and the 

 absence or presence of buds, tiiere seems to be more or less 

 uniformity in the structure of the bristles and hooks as well 

 as of the tubes from pole to pole of the world. It may well 

 be asked why the environment has not altered these organs 

 (bristles and hooks) ? Their functions, it is true, have not 

 altered, but neither have the functions of branchiae or 

 opercula. 



Yet, after all, and taking a broad view of the species, 

 Filograna remains the same, and leads to no other type, for 

 the Spirorbids, which have similar collar-bristles and 

 branchiae, are joined by no intermediate forms, their tubes 

 are coiled and massive, and their opercula larger and 

 calcareous. No change of surroundings in the varied 

 waters stretching from Arctic to Antarctic seas makes the 

 species other than Filograna. Moreover, there does not 

 seem to be any correlation in the parts which vary, even the 

 absence of the opercula and the presence of the enlargement 

 of the tips of the branchial filaments are by no means 



• Darwio, 'Animals and Plants under Domestication,' vol. i. p. 7. 



