140 p. OMODEO 



simple morphology; therefore it is probably very ancient. That makes 

 the point more clear because it is known that other more or less ancient 

 systematic groups (reptiles, fresh water fish and amphibians) have a similar 

 discontinuous distribution in central America and Madagascar since they 

 have found conditions suitable for their survival only in these rather isolated 

 districts. 



At this point we can begin trying to reconstruct the genesis of the profound 

 and undeniable relationship responsible for the fauna of Guinea being more 

 similar to the American fauna than to that of East Africa, and for the 

 Patagonian fauna being almost identical to that of the Cape area but entirely 

 different from that of Paraguay. 



The explanations proposed for problems of this sort can be classified in 

 two categories, which we will call static and dynamic. The static explanations 

 presume that in the past the continents had more or less the same configura- 

 tion and relative position as they do now; the dynamic ones presume that 

 there have been substantial modifications in the configurations of the conti- 

 nents and especially of their relative positions. 



If one admits the stability of the continents, the Amphi-Atlantic relationship 

 of the terricolous Oligochaetes can be explained either by the hypothesis of 

 passive transport across the ocean, or by Matthew's (1915) theory according 

 to which certain systematic groups reached their present centers by radiating 

 from Arctic Circumpolar regions; the subsequent extinction of the northern 

 taxa would have lead to the present discontinuity. 



On other occasions (Omodeo, 1955, 1957) I have maintained that similar 

 interpretations cannot be applied to the earthworms. I am still of the same 

 opinion, but now I am disposed to grant a minimal margin of probability to 

 these interpretations. 



If Simpson (1952) is right in believing that highly improbable events become 

 almost certain given a very long period of time, it is also true that if the 

 probability of an event is nil, eternity will not be enough to make it come true. 

 It is a fact that earthworms, with the exceptions of very few species, have no 

 possibihty of crossing the ocean haphazardly since they do not tolerate 

 immersion in salt water. If they get bathed in it, they die immediately and the 

 same happens to their eggs. 



Their transport across the ocean on rafts or logs is therefore unthinkable, 

 and even if, for the sake of argument, we would accept it as possible, we 

 would still have to explain how they could have crossed the beaches or the 

 wave-beaten rocks on which they were stranded. 



Earthworms and their eggs dwell underground and they do not have any 

 chance of getting stuck to the feet of some birds, and what is more, if they are 

 exposed to the air, they dehydrate and die in a few minutes, or even faster if 

 the air is moving. Thus their transport from one continent to another by 



