2 INTRODUCTION. 



I am also much indebted to the Messrs. WilHams and Dubois, for 

 their skilful and patient labor in the artot}'pe printing, at Newport. 

 There has been no i^etouching of the negatives, although, in sonre cases, 

 a tinted disk has been printed over the plate, by a second impression, 

 as in I. & II. 



Attempts to print in carmine ink, so as to retain the actual color of 

 the stained sections, have not thus far proved successful. 



While a photograph can not often show all that can be discovered 

 by more direct microscopic observation, with a judicious working of the 

 fine adjustment; high authorit}- has stated, and perhaps correctly, that 

 a good photograph, with a low power — say from 3 to 1-2 inch, — is a 

 better means of illustrating the anatomical structure of the nenous tis- 

 sues, than hand drawing. 



Some of the plates, — LXXXI. & XCIV. — with high powers, leave 

 much to be desired both in distinctness and tone ; and in general it may 

 be affirmed that the same defect, as regards distinctness, always exists, 

 and for obvious reasons, in photographs of sections with powers much 

 above 1-2 inch. In fact, it now appears to be established that iinmer- 

 sion objectives can never be employed, for photographing section prep- 

 arations, with the success that has attended their use for blood-corpus- 

 cles, diatoms and similar specimens. 



To give to the student enlarged and exact representations of hard- 

 ened preparations, showing comparative form and dimensions, with as 

 much of the structure as possible, has been the chief aim constantly in 

 view ; and the author will be more than repaid for his labor, if any one 

 of the illustrations, here presented to science, shall prove a help in under- 

 standing the structure of the nen-ous system, or be regarded as an ad- 

 vance in the art of photo-micrography. 



The minute structure of the central nervous system, of many reptiles 



