122 'Journal of Comparative Neurology and Psychology. 



a similar series of observations on the leopard frog, R. pipiens,* 

 was published (Donaldson and Schoemaker 'go). 



In 1902, utilizing the data in both of these investigations, I 

 was able to show that the weight of the central nervous system 

 in both of these species could be calculated by a formula based 

 on the body weight and on the total length of the frog (Donaldson 

 '02). 



For comparison with these results the observations of Fubini 

 ('81) on the European frogs were alone available. 



An examination of Fubini's tables, which are discussed in part 

 in my paper of 1898, referred to above, showed that his findings 

 were so irregular and so different from my own, that it was fair 

 to conclude that he had not worked with sufficient care. 



In order to test this conclusion, I obtained in the spring of 1898, 

 through the courtesy of the Zoological Institute at Zurich, Switzer- 

 land, a series both of R. esculenta and R. temporaria (fusca), 

 all the specimens having been fixed in formalin by a uniform 

 method. A comparison of these specimens with the fresh R. 

 pipiens on the one hand, and on the other with R. pipiens fixed 

 by the same method, indicated that the central nervous system in 

 R. pipiens was heavier than in the European species, and at the 

 same time did not support any of the peculiar findings of Fubini, 

 such as the relatively great weight of the spinal cord. Neverthe- 

 less, limitations in the range in size of the Zurich series and the 

 possibility that the European and American species were differ- 

 ently affected by the fixation treatment, led me to delay publica- 

 tion on this point until fresh material could be examined. The 

 opportunity to do this came in the summer of 1904. In July of 

 that year, through the courtesy of Professor Sherrington, I was 

 able to examine a series of R. temporaria (fusca) in the physio- 

 logical laboratory of University College at Liverpool, England; 

 and in August, through the courtesy of Professor Gaule, a cor- 

 responding series of R. esculenta was examined in the Physio- 

 logical Institute of the University at Zurich, Switzerland. 



In order to eliminate as far as possible, the influence of season 

 on this comparison. Dr. Hatai examined for me, also in August, 

 a series of R. pipiens in the Neurological laboratory of the Uni- 



* In previous papers on the leopard frog, published from my laboratory, this species has been 

 designated as Rana virescens brachycephala. Cope. It now appears that this name is not correct, and 

 that the species in question should be designated Rana pipiens (Schreber) as given above (Donaldson, 

 Science, vol. 26, p. 655, 1907.) 



