6 THE GENUS TRACHELOMONAS, 



Life-history in the Desmidiacece " with regard to the Desmids, 

 and also in "Plankton of the Sydney Water-Supply" with forms 

 of Lagerheimia and Peridinium. While answering very well 

 for genera like Docidium, where the forms comprised in one true 

 species are very much alike, a system of nomenclature which 

 makes each conventional species a variation of the oldest pub- 

 lished type, is inconvenient for general use on account of the 

 intricate and extensive polymorphism that prevails. And this 

 for four reasons : — (l).It seems absurd to make widely differing 

 types variations one of the other, even while admitting their 

 position in the same species. (2). The oldest type is very often 

 not the root-form of the true species, and many of the variations 

 are more closely connected with one another than with the 

 nomenclatural type, so that the system has not even the merit of 

 indicating the exact biological position of the variations con- 

 cerned. (3). So many of the variations have other forms intimately 

 connected with them that it necessitates the frequent use of 

 three-term nomenclature, which is exceedingly cumbrous. (4). 

 The forms biologically connected together in one true species are 

 so widely different in appearance, that only after prolonged ob- 

 servation can the fact of their relationship be determined; and 

 as older and still older forms are correlated, the nomenclatural 

 type keeps changing, to the confusion of the nomenclature. 

 While holding, therefore, just as strongly to the position that 

 the recognised species are mere polymorphic forms (subspecies of 

 vastly broader true species), with regard to the nomenclature, I 

 have returned to the generally accepted scheme. I see no reason 

 why, for convenience' sake, we should not work in species which 

 are frankly conventional, provided that the true state of affairs 

 in Nature is freely recognised. The species, it is true, is a 

 biological entity, not a conventional one, but the polymorphism 

 of the lower orders of microscopic vegetable and animal life being 

 as wide-spreading as it is, it is impossible to reconcile the exi- 

 gencies of nomenclature (simplicity and conciseness) and biology 

 (true connection of forms by life and growth) so that the name 

 of an organism shall be the index of its biological position in 

 Nature. 



