August 23, 1883] 



NATURE 



395 



which comes up if the material shall be of any use to 

 zoogeography. 



Having indicated my views in general on this subject, 

 [ will proceed to state those cardinal points of which the 

 zoologist should always give exact and as detailed parti- 

 culars as possible, which I consider essential to the 

 development of zoogeographical science. They are : — 



1. Place of Discovery. — This should preferably be fixed 

 by latitude and longitude, but, if this is not possible, by 

 other exact means. In works describing certain sea fauna I 

 have often found expressions as vague as these : " Bo- 

 huslan (province of Bonus) — Bergen," or " Kullen — Fin- 

 marken," "Norway and Greenland." The former of these 

 descriptions may be satisfactory enough, if thereby is 

 meant that the species in question are to be found be- 

 tween Bohuslan and Bergen, and from Kullen to Fin- 

 marken, although it would have been of more value if, 

 even with the commonest kind, each place of discovery 

 had been enumerated. It is a well-known fact that both 

 common and rare species alike are found in smaller or 

 larger quantities in different places, and it is information 

 of this circumstance which it is necessary to have if a 

 student shall be able to determine the horizontal exten- 

 sion of a certain species and its numerical relation to 

 others within a certain area. With regard to the latter it 

 implies, I suppose, that the species in question may be 

 found along the whole coasts of Norway and Greenland, 

 but the real meaning is, however, that they have been 

 found somewhere, perhaps in several places, within the 

 specified limit, and information of su:h vague character 

 is to say the least of it imperfect. The physical condi- 

 tions of the coasts of Greenland below the level of the 

 sea may be the same from the most southern to the most 

 northern point, but, on the other hand, it must not be 

 forgotten that the known extent of Greenland from south 

 to north is 23 degrees, i.e. 345 geographical miles, and 

 that it is, therefore, just as likely that what applies to 

 the development of the fauna in Davis Sound does not 

 apply to that in Baffin's Bay ; less still in Smith's Sound, 

 not to mention that of the east coast. The extent of 

 Norway covers 11 '5 degrees, or 172 geographical miles, 

 and the physical conditions around the coast are very 

 variable, and as regards the fauna of the sea here it is a 

 fact that there is a great division in the southern and 

 the arctic element. 



An exact fixing of the place of discovery has only been 

 quite recently effected. Thus, K. Moebius's work, " Die 

 wirbellosen Thiere der Cstsee," F. Meinerts's " Crustacea 

 isopoda, amphipoda, et decapoda Daniae," and A. \Y. 

 Ljungman's " Forteckning ofver Spetsbergens Holo- 

 thurider " leave nothing to be desired in this respect ; 

 but these cases are only exceptional, as most zoologists, 

 whether treating the anatomy or the fauna, are satisfied 

 with a mere enumeration of places of discovery. It is, 

 however, true that zoological literature, as well as all 

 other, deals with many extraneous matters, while some 

 writers are anxious to adopt a very brief style ; but in 

 the matter of detailing the place of discovery no brevity 

 should be observed. If zoogeography is to be something 

 more than a mere knowledge of the horizontal distribu- 

 tion of the species, the places of discovery must be exactly 

 detailed. 



2. The Depth. — The depth at which the sample was 

 taken should also be exactly stated as, while the place of 

 discovery teaches us the horizontal distribution of a species, 

 the depth indicates the vertical one. It is a well-known 

 fact that most species are confined within certain vertical 

 limits, which are in some instances not far apart. It cer- 

 tainly was to be expected that information of this nature 

 would be found in modern works, but this is not the 

 case. G. O. Sars' " Mollusca regionis arctica Nor- 

 vegia," F. Meinerts's above-mentioned work, and O. 

 Harger's " Report on the Marine Isopoda of New Eng- 

 land and Adjacent Waters" are, however, remarkable 



exceptions to this fault. The accuracy and minuteness of 

 these authors on the vertical distribution of the species 

 deserve every commendation, while it must be regretted 

 that such a work as A. Bocck's " De tkandinaviske og 

 arktiske Amphipoder," which is undoubtedly the fruit of 

 many years' practical study and research, gives in most 

 cases no account whatever of the vertical distribution of a 

 species. One attempts thus, for instance, in this work 

 unsuccessfully to learn within what limits such a common 

 species as the Gammarus focus/a occurs on the Scandi- 

 navian coast. R. M. Bruzelius, in his work, "Skandi- 

 naviens amphipoda gamonaridea '' (185S), and A. Goes, 

 in his "Crustacea amphipoda maris Spetsbergiam all- 

 nentis, &c." (1865), had both set excellent examples in 

 the way of describing the distribution of species in the 

 deep ; still Boeck has paid no attention to this important 

 question. He has only dealt with the synonymy, genus, 

 and the horizontal occurrence of the species, and even as 

 regards the latter his statements are very summary. With 

 such statements as these, that Diastylis Rathkei has been 

 found between 3 and 540 fathoms, Idothea Sabieni between 

 4 and 1 21 5 fathoms, Axinus jlcxuosus between 3 and 450 

 fathoms, Xylophaga dorsalis between 10 and 650 fathoms, 

 and Caryophyllia Peurtalesi at 100 and 980 fathoms 

 depth respectively, it may at first sight appeara matter of 

 little importance to state at what depth they have in each 

 individual case been found. This is, however, one of 

 great importance. The vertical distribution of species is 

 variable in different seas, and it must depend on subse- 

 quent research to determine on what this variability de-. 

 pends. The causes may be several, and are no doubt 

 complicated ones, as the pressure of the water, which for 

 a long time was considered one of them, does not in any 

 way affect their existence. The causes must be of a very 

 different nature, and before any of them can be ascer- 

 tained it is necessary to obtain exact particulars of indi- 

 vidual instances. The following comparison of the 

 vertical distribution of a few species in various seas may 

 illustrate this : — 



Tellina solidula appears in the Arctic waters of — 



Novaya Zemlya Norway 



at from 4- 26 fathoms at from o- 10 fathoms 

 Cardinal cilia 'uni 

 Cardium gronlan- \ 



dicum j 



Rhynchoiicllapsit- \ 



tacca \ 



Margarita obscura 

 Fusus tornatus 



The difference in five of these cases is not very great, 

 but in one — Margarita obscura — it is very considerable, 

 and even if we are unable to explain it, it should neverthe- 

 less be recorded. 



3. The Nature of the Bottom. — This is a factor of 

 great moment in the fauna of the sea and the division 

 of the species. I have thus on the coast of Novaya 

 Zemlya and in the Siberian seas personally observed 

 that a clean sand bottom without admixture of clay 

 is very poor in fauna, but if mixed with some clay some- 

 what richer, while where the clay predominates it is 

 greatly richer. The most copious and varied is, however, 

 that of the pure clay bottom. In shallow water on the 

 coasts of Scandinavia the student has many opportunities 

 of observing the variations in the copiousness of the sea 

 fauna, both as regards the numerousness of the species 

 and their individuals on bottoms of various natures. 

 Possibly the nature of the bottom at greater depths, 

 below the line where the higher orders of Algae cease to 

 exist, is not of such influence as above the same, but that 

 it is in most instances of great moment to the fauna I 

 am firmly convinced. To animals which do not live 

 on prey the quantity of the organic elements in process 

 of decomposition in their place of vegetation must be of 

 consequence ; to most of them the organic composition 



