of the Larvce of Marine Animals. 405 



simple question, before which all others are of little moment : 

 How many days can the various larvte of the benthos animals 

 live in the phuiicton ? 



To this question we may seek an answer by two means. 

 First, we might take the faunas of a series of coral or recent 

 volcanic islands, and comj)are them with the faunas of the 

 nearest land-masses, or, better, of such land-masses as are 

 swept beforehand by the currents which reach their shores. 

 We may thus compare the littoral fauna of Bermuda with 

 that of the Tortusjas or Bahamas, or even the West Indies 

 in general. We shall get certain positive results of 

 utility, but those really valuable for our purpose should be 

 negative. Certain littoral animals, and even groups of 

 animals, will not be found. We say that their larva have 

 not been able to live long enough to reach Bermuda ! But 

 is the temperature suitable? Surel}' Bermuda is mainly 

 corallaginous, while the West Indies are largely volcanic, 

 and in any case the bottom deposits of the latter are rich in 

 silica ! The West Indies are continental and have, as com- 

 pared with Bermuda, a far richer food-supply! In effect the 

 environment of the two localities is absolutely diiferent, and 

 our inquiry at first sight seems futile. 



Perhaps the case of Bermuda and the West Indies is an 

 extreme instance, v/here the conditions are widely diverse, 

 but yet in respect to any islands or groups of islands in the 

 Pacific the same arguments could be put forward, and in no 

 instance that I am at present aware of could be properly con- 

 futed as regards banks more than 100 miles apart. Let 

 not this, however, nor any other method of inquiry be 

 despised ! It is capable of results of some considerable 

 value. Has our shore or that of Norway, of France, or of 

 Spain, any of the characteristic animals of the West-Indian 

 littoral fauna? In this instance a thousand conditions 

 perchance are diffi^rent ; but why does the Indo-Pacific fauna 

 reach to the Sandwich group, tlie Marquesas, and the 

 Paumotus, and yet fetch no part of the American shore? 

 The method may, indeed, give us differential results as we 

 travel eastward in the Pacific Ocean or compare the faunas 

 of the Azores, the Canary ox Cape Verd groups with those 

 of the nearest West-Indian banks. Some \^'est-Indian 

 genera, families, and even groups, maybe, are absent from 

 the Western-Atlantic banks ; other families are present, but 

 their genera are different; yet in others we may find the 

 same genera but the species are different ; and, lastly, in 

 still others the species are identiciil. 



The critics of our views on distribution will, perhaps, and 

 Ann. 6c Mag. N. Hist. Ser. 7. T o/. xiv. 29 



