678 SCIENCE PROGRESS 



which a part separated off dies at once and the power of re- 

 generating specialised cells has almost disappeared. 



Now cancer appears to occur only among the vertebrates, in 

 which group of organisms somatic co-ordination is more perfect 

 than in any of the organisms from which they are generally 

 supposed to have been evolved 1 and in which the general 

 potentiality of the cells for regeneration reaches its lowest ebb. 

 In these organisms it would appear that when the cells pass out 

 of somatic co-ordination while still remaining connected with the 

 body in which they occur, excluding of course the reproductive 

 cells which are thrown off, they continue to multiply and behave 

 to some extent as independent organisms, though they no longer 

 possess the capacity of undergoing differentiation necessary to 

 produce a new individual similar to the organism from which 

 they arose. In plants — in which, apparently, cells may be 

 thrown out of somatic co-ordination by artificial stimuli (apospory 

 and apogamy) — the cells proceed to form new and complete 

 individuals. It seems then probable that the behaviour of the 

 cells forming malignant growths after having passed out of 

 somatic co-ordination is due to a diminution of the general 

 power of undergoing differentiation in the progeny of the 

 specialised tissue cells of the vertebrate body and the increase 

 in the general influence of somatic co-ordination in these animals, 

 which is perhaps partly due to the presence of their particular 

 form of nervous system. 



Personally I have great doubts as to whether cancer really 

 occurs in any animals other than mammals. Several instances 

 in which numbers of fish were stated to have developed cancer 

 in particular fish-cultural establishments have proved to have 

 been growths due to parasites. The extraordinary similarity in 

 microscopical appearance— particularly in the case of the ordinary 

 pathological preparation — between cancer and certain growths 

 produced by parasites throws great suspicion upon the other 

 cases described as occurring in fish and upon the few described 

 as occurring in amphibia. The so-called cancers in fish and 

 amphibia have not been sufficiently investigated and if the 

 existing observations have been misinterpreted, the theories 

 advanced here will be strengthened rather than weakened, as 

 among mammals somatic co-ordination appears most perfectly 



1 Arthropods, etc., are excluded from this theory as probably not being in the 

 direct line of evolution of the vertebrates. 



