2 Mason- — Central Nervous System, of Reptiles^ etc. 



ened specimens, it is especially well adapted for measurement, 

 and its prominence as an object in the microscopic field seems 

 constantly to invite our eiforts to determine more about its 

 real nature and fnnction. The writer does not claim to have 

 accomplished much in this direction. The facts, however, 

 which he has brought to light have been established with so 

 much care and precision that he feels warranted in formulat- 

 ing the following law, which he predicts will be found to hold 

 true in all vertebrate animals, viz.: 



The nuclei of the cells in the inferior {anterior) horns, in 

 the two enlargements of the spinal cord, have average diame- 

 ters which are proportio7ial to the muscular 'power of the cor- 

 responding extremities. 



The observations which seem to justify the above law are 

 briefly the following: 



In the frog, which uses almost exclusively its posterior 

 extremities for locomotion, on land and in water, I find that 

 the average diameters (for liana halecina) of the cell-nuclei of 

 the crural enlargement exceed, by abont -^^-j^ of a millimetre, 

 the average diameters (long and short) of the cell-nuclei of 

 the brachial enlargement. The average size of the former 

 stands to that of the latter very nearly in the arithmetical 

 ratio of 7 to 6 divisions of the micrometer eye-piece used with 

 Nachet's objective, No. 5. 



In the gopher of Florida, testudo polyphemus (Molbrook), 

 which lives exclusively on land, and digs deep excavations in 

 the earth with its anterior extremities, the latter become quite 

 powerful, and attain a development more than double that of 

 the posterior limbs. The average diameters of the cell-nuclei 

 in the spinal cord of this animal I have found to have a re- 

 verse arrangement as to size from that noticed in the frog. 

 The average size of the brachial nuclei stands to that of the 

 crural nuclei in the arithmetical ratio of about 7.5 to 7. 



In other words, there was a diflference in the diameters of 

 about 7f^^ of a millimetre, the nuclei of the cells of the an- 

 terior or brachial enlargement beino: larger than those of the 

 posterior or crural enlargement. 



Again, in the so-called terrapin of the St. John's river, Flor- 



