Donaldson, American and European Frogs. 147 



2. A heavier brain and spinal cord. 



3. A heavier brain in proportion to the weight of the spinal 

 cord. 



4. A greater percentage of water in both the brain and spinal 

 cord. 



5. A larger number of both sensory and motor medidlated 

 fibers in the spinal nerves (when compared with R. esculenta). 



6. A slightly greater proportion of sensory fibers in the spinal 

 nerves (when compared with R. esculenta). 



7. Shorter internodes, and therefore a greater number of sheath- 

 ing cells (when compared with R. temporaria). 



With the possible exception of the percentage of water, the 

 interpretation of which is not yet clear, all these characters may 

 be counted to the credit of R. pipiens as indicating a higher devel- 

 opment of its nervous system, and if we may make these charac- 

 ters a basis for physiological predictions, we should expect the 

 American leopard frog, R. pipiens, when compared with the Euro- 

 pean, R. esculenta and R. temporaria, to give (i) more perfect 

 general reactions associated with (2) less perfect reflex ones, and 

 also to be both (3) stronger and (4) more sensitive. 



APPENDIX. 



The observations of Fubini, '8 1. 



In 1881 Fubini published, under the title "Gewicht des Cen- 

 tralen Nervensystems im Vergleich zu dem Korpergewicht der 

 Thiere bei Rana esculenta und Rana temporaria," a study of 

 the weight of the brain and spinal cord in the two European species 

 commonly used for experiment. His data are comprised in eight 

 tables, each sex being represented by four tables, and the records 

 on twelve specimens entered in each table. His main object in 

 this study was to show that in the female frog, the weight of the 

 central nervous system was less than in the male. As I have 

 elsewhere explained (Donaldson and Schoemaker, 'go), he 

 does not show this, having fallen into error by reason of his failure 

 to appreciate that the relative weight of the central nervous system 

 diminishes with the increasing body weight of the frog. 



Despite this failure in the interpretation of his records, it was 

 desirable to examine further his original tables in order to deter- 



