32 David Starr Jordan 



We should know also in each group which are the ancestral 

 or primitive forms. We should know whether the arctic 

 members of any group are those primitively of many segments, 

 or whether their characters are due to degradation through 

 "Panmixia," or from other cause. This investigation should 

 be extended to each group, and the answers in different 

 groups may be different. 



The analogy of the reduction in number and the specializa- 

 tion of the individual vertebrae and fin raj'S, to the reduction 

 and specialization of wing-veins in I^epidoptera, as shown by 

 Professor Comstock should be studied. The resemblance of 

 the results of evolution in Fishes and Insects indicate a like- 

 ness in the causes. 



The correlated changes in the brain and nervous system 

 should also be studied. Mr. Frank Cramer has suggested to 

 me that the process of " Ichthyization " should have given 

 tropical forms larger and more specialized cephalic ganglia. 

 To this end, the size and form of brain in Sebastes, Sebastodes 

 and Scorpana should be carefullj? studied. Similar studies in 

 the LabridcE, Pleuronedida: , Blenniida and Lophiida ought to 

 yield interesting results. 



It will be also interesting to know whether anj- analogous 

 changes have taken place in any other groups of animals as 

 Suakes, L,izards, Batrachians, Crabs, Centipedes or Insects. 

 But among land-animals it will not be surprising if the results 

 are different for the conditions are not quite parallel. With 

 fishes the greatest tropical heat of sea-water is never too 

 great for comfort, nor is it often greater than the natural 

 temperature of the fish. The heat of the land is often much 

 greater than this and it may be so great as to interfere with 

 individual growth of land animals, and it may thus check 

 competition instead of stimulating it. 



In any event, a comparative study of the relations of seg- 

 ments to temperature in any group cannot fail to yield inter- 

 esting results. 



HISTORICAI, SKETCH. 



Gihither, 1862. — The earliest observation on record in refer- 

 ence to the subject in question was made by Dr. Albert Giin- 



