Mason — Central Nervous System of Reptiles, etc. 3 



i(la, Emys F]oridana(Holbrook), which uses the posterior with 

 much greater effect than the anterior extremities in swimming-, 

 and which has correspondingly large hind legs, the arrangement 

 of nuclei as to size is reversed in accordance with the law. The 

 difference in the average diameters I here found to he less than 

 in the nuclei of the gopher; but, whereas in the latter animal 

 the brachial nuclei were found to be larger than the crural 

 nuclei, in the erajs the nuclei from the crural enlargement 

 were the larger. 



I have also measured these nuclei in the spinal cord of 

 alligators; red-headed lizards, Scincus erythrocephalus (liol- 

 brook); horned toads, Phrynosoma cornutum ; and the chamele- 

 ons of the South, Anolius Carolinensis, without being able to 

 detect constant differences in average diameters between these 

 elements from the two enlargements. Only in the frog and 

 the two species of chelonia referred to, have I found a marked 

 disparity between the brachial and the crural nuclei. This 

 equality of the nuclei in lizards seems, therefore, confirmatory 

 of the law which I hope to have established, for of all the 

 animals above enumerated, frogs and turtles present the 

 greatest inequality in the extremities as to size and especially 

 as to power. 



In the alligator and lizards, while the posterior are consid- 

 erably larger than the anterior extremities, the difference, if 

 there be any, in the power which can be exerted by the two 

 sets of limbs in running or climbing, is inconsiderable when 

 compared with the marked contrast in their functions to be 

 observed in the frog, gopher and emys. 



The diameters of the nuclei of the nerve-cells vary in differ- 

 ent individuals of the same species, in accordance with the age 

 of the animal. Thus, in a very small but well-developed and 

 active specimen of Rana halecina, I found the average diame- 

 ters of inferior horn groups from all parts of the coi'd to be 

 less than those in another specimen of this species, about 

 three times as large. The crural nuclei, however, were found 

 to be larger than the brachial nuclei in both animals. In a 

 young gopher, which had not yet used its anterior limbs for 

 burrowing, the nuclei in general were smaller than those of a 

 full-grown animal, while I could discover no difference in size 



