AMPHIPODA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 177 



was little opportunity of distinguishing between characters subject to individual variation 

 and those really common to the species. Consequently, when other specimens were 

 obtained it was frequently found that they did not agree in all particulars with any of 

 the species already described, and they were naturally considered to be new and were 

 given a distinctive name. This practice was perhaps the safest at the time, and it was 

 the more desirable when the specimens came from a new locality ; but it unfortunately 

 led to the idea that forms from fresh localities were almost necessarily new, and that 

 the distribution of nearly all the species of Amphipoda was very limited. It also led 

 to the introduction of long specific diagnoses, often containing characters of individual 

 importance only. Naturally enough, specimens afterwards examined did not agree in all 

 respects with these detailed descriptions, and thus a vicious circle was set up, leading to 

 the continued establishment of new species, some of them being admittedly described in 

 self-defence, and the fact that many species were widely distributed was long obscured. 



As knowledge gradually increased it was found that in many cases the same species 

 had been described under various names, and the preparation of a general survey of 

 the whole group, such as that for Das Tierreich, necessarily led to a considerable 

 reduction of species. From the example of a few species which were readily recognised, 

 and hence known to occur at places widely remote from one another, it was found that 

 some species at any rate were more widely distributed than had been originally 

 supposed. Much assistance in clearing up difficulties was obtained from the detailed 

 study by various authors of individual species and the consequent elucidation of the 

 various forms that occur in some species and especially of the differences between the 

 sexes and of the changes that take place during growth ; and it is to further work of this 

 kind that we must look for assistance in defining the limits of the different species. 



Several of the species or groups that I refer to under one specific name are 

 widely distributed in sub-Antarctic seas, and, as might be expected, the specimens from 

 different localities now separate from one another are not always precisely the same, but 

 show what may be considered local varieties. Some authors would doubtless prefer to 

 call these local varieties species and give each a distinctive name ; but this must 

 necessarily lead to an indefinite multiplication of species, with ever-increasing difficulty 

 of determining those already established, and as a matter of practical convenience it 

 seems to me to be better at present to endeavour to recognise these widely distributed 

 species and to leave the determination of their varieties until a larger number of forms 

 from many localities have been studied. 



In the list below I have indicated briefly the distribution of each species. From this 

 it will be seen that an increasing number are now known to extend around the globe in 

 sub- Antarctic seas, and that there is a greater resemblance between the Amphipodan 

 faunas of South America, New Zealand, Australia, Kerguelen Island, and even South 

 Africa, than appeared to be the case a few years ago. The importance of the facts 

 on the question of the cause of this distribution cannot be discussed here. Another 

 point made clear is that the number of species in northern seas represented by the same 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 459.) 



