Mason — Central Nervous St/siem of Reptiles^ etc. 5 



counted, and the eye made t'amiliar with tlieir relative })Osition 

 in tlie field, in order to avoid measuring the same nucleus 

 twice. The measurements as taken are noted down for this 

 horn, and then the horn of the other side of the section is 

 brought into the field, and so with each section on the slide.* 

 The process is somewhat laborious, but by properly dividing 

 the work it may be gone throngli with without much fatigue. 

 After all the measurements that are desired are taken, they 

 are added together and the sum is divided by the number of 

 nuclei measured. This gives the average diameter. 



Example. 



Measurements op Nuclei from the Spinal Cord of Testvdo poly- 

 PHEMUS No. 1. May 15th, 16th and 17th, 1880. 



The above diameters are in divisions of the micrometer eye-piece with 

 Nachet No. 5 — 7 divisions being equal to .0175 m.m. 



* It is often possible to mount as many as twelve sections on the same slide. 



