F. Borgesen: General remarks. 485 



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184. Chrysymenia Agardhii Harv. 



185. — planifrons (Melv.) J. Ag. 



186. — ventricosa (Lamour.) J. Ag. 



187. — Enteromorpha Harv. 



188. — pyriformis Børgs. 



189. — Uvaria (L.) J. Ag. 



var. occidentalis Børgs. 



190. Coelarthrum Albertisii (Piccone) Børgs. 



191. Champia parviila (Ag.) Harv. 



192. — salicornoides Harv. 



General remarks. . 



Definition of Species. 



It is a well-known fact that some species show wide variation 

 while others are almost constant and do not offer any difficulty 

 as to classification. 



Whilst the classification favoured by some writers tends to 

 the formation of many small species in spite of the fact that inter- 

 mediate forms occur between them, others prefer to group into 

 more comprehensive species those forms which are linked together 

 by intermediate stages. It appears to me that the middle course 

 is here the most convenient. When I have considered myself 

 able to prove the existence of such intermediate forms I have 

 thought it best to refer them to the species with which they have 

 most in common. 



But in order to finally decide the matter an extensive mate- 

 rial is necessary. When the material at hand contains only few 

 specimens it is safer to classify into separate species; they can 

 always, when more material is at disposal, be united later, if ne- 

 cessary. 



To take an instance from the West Indian algæ, I have pointed 

 out that Caiilerpa ciipressoides is a very variable plant, the forms 

 of which are very diverse, but nevertheless these are all refe- 

 rable to the same species, as the variations seem to be due to 

 the environment and are connected with intermediate forms. 



