Septembeb 4, 1908] 



SCIENCE 



313 



reviewer has already in part expressed his 

 opinion' and Dr. Eastman's renewed argu- 

 ments have not led him to alter his point of 

 view. 



The central argument against Dr. East- 

 man's theory of the dipnoan affinity of the 

 Arthrodira seems to the reviewer to be that 

 he lays too much stress on a single character 

 — the resemblance of the crushing dentition 

 of the eeratodonts to that of Mylostoma 

 among arthrodires. This resemblance he in- 

 terprets as an homology and makes it one of 

 the cardinal arguments for relationship. But 

 why may not this partial resemblance in den- 

 tition be a case of parallelism, of adaptation 

 to similar food, in two widely different groups ? 

 — especially so in view of the wide differences 

 between arthrodires and dipnoans in other 

 regards, and because of the frequent occur- 

 rence among fishes of adaptations to a similar 

 hard diet. It seems to the reviewer that a 

 close examination of Dr. Eastman's argument 

 for the homology of the ceratodont and ar- 

 throdiran dentitions, especially the exposition 

 on pages 150-161, will hardly carry convic- 

 tion to the mind of the critical reader. 



But the establishment of homology between 

 ceratodont and arthrodiran dentitions is the 

 crucial point in Dr. Eastman's theory. Re- 

 ject this central argument as not proved or, 

 if you please, as sub judice, and little evi- 

 dence remains, at least in the reviewer's 

 opinion, to support the thesis of a genetic 

 affinity between arthrodires and dipnoans. 

 Some of the adduced evidence must, in fact, 

 be ruled out of court as not material to the 

 present case, for instance the question of the 

 shape of the caudal fin' or of the homology 

 of certain skeletal elements. 



Furthermore, as Professor Dean has re- 

 cently urged, there axe certain absolutely irrec- 

 oncilable differences between arthrodires and 

 subject see a review by Professor Bashford Dean 

 in Science, July 12, 1907, p. 48. 



' Mem. Amer. Mus. Nat. Eist., IX., 1906, pp. 

 126-128. 



' For, granted even that Coccosteus had a di- 

 phycereal tail, and that fact does not alter the 

 balance of evidence, since a diphycercal tail is not 

 an exclusively dipnoan character. 



dipnoans; for instance, the presence in all 

 arthrodires of a complicated dorsal and ven- 

 tral body-armor constructed on one plan and 

 with complicated neck joints, and its absence 

 in all dipnoans. 



And again, the characters linking the 

 arthrodires with the Ostracophores to which 

 writers have again and again called attention 

 within the past half century, are surely not 

 dipnoan. 



These are only some of the broader criti- 

 cisms against Dr. Eastman's views on the 

 affinity of the arthrodires. Did space permit, 

 we might profitably examine certain of the 

 subsidiary hypotheses and conclusions and 

 point out minor difficulties and discrepancies 

 which weigh against Dr. Eastman's main 

 thesis. But enough has been said, we believe, 

 to indicate some of the chief grounds for 

 dissenting from our author's view that the 

 Arthrodira are specialized dipnoans. 



l. hussakop 

 American Museum of Natubal History 



Variations and Genetic Relationships of the 



Garter Snakes. By Alexander G. Ruth- 



VEN. United States National Museum, 



Bulletin 61, pp. 201. 1908. 



In these days of minute analysis on the part 



of systematic zoologists, an acute and exact 



study of variation with a synthetic purpose 



comes as rest to the weary. 



The courage displayed by Dr. Euthven in 

 giving reasons for his scheme of genetic rela- 

 tionships in this impracticable group can be 

 best valued by other herpetologists who have 

 ventured on the same task and have been 

 carefully secretive as to how they did it. Aa 

 one of these I may be privileged to both 

 praise and criticize this excellent paper. 



Nothing but good can be said of the method 

 adopted by the author in carefully estimating 

 the value of the characters commonly held to 

 be specific in snakes, and of the painstaking 

 care with which it has been followed to the 

 end. It is an ingenious bit of demonstration, 

 and one easily verifiable, which shows that 

 reductions in the number of rows of dorsal 

 scales as girth of body decreases in the in- 



