THE BIOLOGIST POSES SOME PROBLEMS 89 



family, the Desmomonadinaceae, which has obvious evolutionary 

 euryhaHne characteristics. The green algae show both fresh and 

 salt water branches, but the terminal groups seem either one 

 thing or the other, while the lower groups retain much evolutionary 

 euryhalinity. The same situation certainly is reflected in the less 

 well documented evolution of Foraminifera. In view of the general 

 lability of all the lowest protist groups we may expect a similar 

 history for the purely marine but very specialized Radiolaria and 

 Acantharia. 



If we adopt the Hadzi-Hanson type of phylogeny for the 

 metazoa, marked evolutionary euryhalinity is retained by the 

 ciliates into the lower flatworms ; if we adopt the more conventional 

 Haeckel-Hyman theory of a coelenterate ancestry, the evolutionary 

 euryhalinity is lost by the time the metazoa appear. Thereafter 

 we have in the animal kingdom great lineages of marine forms, 

 with occasional production of limited groups capable of invading 

 freshwaters. In the higher forms this occurs in a very super- 

 dispersed way. Almost all the cases in the Polychaeta, for instance, 

 are in the Nereidae or Fabriciinae as Hartman (1938) points out. A 

 single invasion into freshwater from the whole range of deu- 

 terostome phyla is all that is certainly needed to explain the early 

 habitats of the vertebrates, but this implies much migration back- 

 wards and forwards after a freshwater fish fauna was well estab- 

 lished. Parenthetically it appears to the present writer that the 

 evidence for a freshwater origin of the vertebrates per se is quite 

 unconvincing. If that marvellous but almost completely ignored 

 fossil Ainiktozoon loganense Scourfield (1937) is what it looks like, 

 namely, a late surviving missing link between the tunicates and 

 the true vertebrates, it certainly does not indicate a rheophil 

 type of organization, but rather something living pelagically like 

 a salp or Velella but with additional directional mobility. This 

 mode of life would accord with the presence of a number of speci- 

 mens in the Ceratiocaris horizon, presumably blown inshore into a 

 lagoon, just as I have observed Velella blown up the artificial 

 channel that connects Lake Avernus, west of Naples, with the 

 sea. 



If we now try to interpret the data presented by the general 



