548 



SCIENCE. 



[N. S. Vol. XIV. No. 354. 



SIGNIFICANCE OF RESEMBLANCE. 



The significance of these facts can be 

 shown only by a fuller analysis of the fauna 

 in question, and those of other tropical and 

 semi-tropical waters. If the resemblances 

 are merely casual, or if the resemblances 

 are shown by other regions, the hypothesis 

 of shore continuity would be unnecessary 

 or untenable. It is tenable if the resem- 

 blances are so great as to be accounted for 

 in no other way. 



Of the genera regarded as common, only 

 two* or three are represented in the two 

 regions by identical species, and these have 

 a very wide distribution in the warm seas. 

 Of the others, nearly all range to India, to 

 the Cape of Good Hope, to Australia or to 

 Brazil. They may have ranged farther in 

 the past ; they may even range farther at 

 present. At the most, but twof are con- 

 fined to the two districts in question. 

 As equally great resemblances exist between 

 Japan and Australia or Japan and the 

 West Indies, the case is not self-evident, 

 without fuller comparison. I shall, there- 

 fore, ask your attention to a somewhat 

 fuller analysis of the evidence bearing on 

 this and similar problems, with a view to 

 the conclusions which may be legitimately 

 drawn from the facts of fish distribution. 



DIFFERENCES BETWEEN JAPANESE AND 

 MEDITERRANEAN FISH FAUNAS. 



We may first, after admitting the alleged 

 resemblances and others, note that differ- 

 ences are equally marked. In each region 

 are a certain number of genera which we 

 may consider as autochthonous. These 

 genera are represented by many species or 

 by many individuals in the region of their 

 supposed origin, but are more scantily de- 

 veloped elsewhere. Such genera in Mediter- 

 ranean waters are Crenilabrus, Labrus, Spi- 

 cara, Pagellus, Mullus, Boopis, Spondylosoma, 



* Beryx, Hoplostethus and perhaps Macrorham- 

 phosus. 



f Lepadogaster, Myrus. 



Oblata. None of these occurs in Japan nor 

 have they any near relatives there. Jap- 

 anese autochthonous types, as Pseudoblen- 

 nius, Duymceria, Anoplus, Histiopterus, Mono- 

 centrus, Oplegnathus, Plecoglossus, range south- 

 ward to, the Indies or to Australia, but all 

 of them are totally unknown to the Med- 

 iterranean. The multifarious genera of 

 Gobies of Japan show very little resem- 

 blance to the Mediterranean fishes of this 

 family, while blennies, labroids, scaroids 

 and scorpsenoids are equally diverse in their 

 forms and alliances. To the same extent 

 that likeness in faunae is produced by con- 

 tinuity x)f means of dispersion, is it true 

 that unlikeness is due to breaks in con- 

 tinuity. Such a break in continuity of 

 coast-line, in the present case, is the Isth- 

 mus of Suez, and the unlikeness in the fau- 

 nas is about what such a barrier should pro- 

 duce. 



SOURCES OF FAUNAL RESEMBLANCES. 



There are two main sources of faunal 

 resemblances ; first, the absence of barriers 

 permitting the actual mingling of the spe- 

 cies ; second, the likeness of temperature 

 and shore configuration favoring the de- 

 velopment of the same or analogous types. 

 If the fish faunae of different regions have 

 mingled in recent times, the fact would be 

 shown by the presence of the same species 

 in each region. If the union were of a 

 remote date, the species would be changed, 

 but the genera might remain identical. 



In case of close physical resemblances in 

 different regions, as in the East Indies and 

 West Indies, like conditions would favor 

 the lodgment of like types, but the resem- 

 blance would be general, the genera and 

 species being unlike. Without doubt, part 

 of the resemblance between Japan and the 

 Mediterranean is due to similarity of tem- 

 perature and shores. Is that which re- 

 mains sufficient to demand the hypothesis 

 of a former shore-line connection ? 



