NUCLEI IN THE NERVE CELLS. 24 



examined, and in the spinal cord of the frog and gopher turtle, in which 

 animals the number of muscles is practically the same for both pairs of 

 extremities. 



It is possible that a correspondence also exists between the number 

 of nuclei (or cells) and complexity of function, or number of muscles. 



Plates XCIX. — CXIII. simply illustrate a few of the most promi- 

 nent facts in regard to the comparative dimensions of nuclei, no claim 

 being made that these photographs from single sections demonstrate the 

 average which has been obtained by the study of a large number. The 

 nuclei in the cells of origin of the oculomotorius are remarkabi}' well 

 shown in Plate CX. and may be satisfactorily compared with those in 

 Plate CXI. — origin of the motor root of the trigeminus — snapping turtle. 



I have photographs which show these nuclei from the iguana indi- 

 cating a difference of the same kind, but less in degree. 



The numbers in parentheses, at the close of the list of plates, will 

 enable the reader to find those photographs which have been taken from 

 the same individual and with the same magnifying power. 



No sympath}- with any theory which claims to distinguish between 

 motor and sensory cells is here implied, nor does the writer insist upon 

 any special anatomical importance for the nuclei, as compared with the 

 cell bodies, beyond their more distinct and regular outline which makes 

 them very conspicuous and hence well adapted to accurate micrometric 

 observation. That the nuclei are the true functional centres of the 

 nerve cells is at best an unproved hypothesis ; but comparative meas- 

 urements of these bodies are facts which seem very essential to the fu- 

 ture understanding of their function. 



