EVOLUTION OF FOSSIL CEPHALOPODA. 251 
has shown us the way; Branco, by his studies of the 
larval stages of ammonoids, has accumulated a great 
mass of accurate data that can be used with confidence, 
even by the student that rejects his theories as to classi- 
fication, And Karpinsky, by using the methods and 
principles discovered by these naturalists, has worked 
out the genealogy of one of the chief stocks of the 
earlier ammonites. This way lies the truth, and not in 
groundless speculations such as many students of cepha- 
lopods are prone to indulge in. 
In order to succeed, one must select material with 
great care, preferably limestone that is soft but not so 
weathered as to crumble, nor so brittle 
as to shatter. One’s finger nail and 
some steel dental chisels are all the 
tools needed for breaking off the outer whorls of young 
ammonites, A microscope with thirty diameters magni- 
fying power is the most satisfactory, although higher 
powers are occasionally needed. For studying surface 
markings a strong pocket lens is usually sufficient; the 
specimen should then be placed dry on white cardboard. 
For observing the sutures, or shape of the whorls, the 
specimen should be placed on cardboard in a drop of 
water, spread out so as not to distort the object. The 
water, being slightly viscous, will also hold the small 
object in any position. For taking measurements a 
micrometer eyepiece is needed, especially in drawing, 
for the camera lucida is not very satisfactory for draw- 
ing opaque objects. Sections can easily be cut by 
grinding with emery powder on a glass plate. 
The accompanying illustrations will give an idea of 
how the facts are ascertained. A number of well-pre- 
served adults of a species are selected, and the outer 
coils are pulled off piece at a time under water, until a 
complete series is obtained, representing every change 
Method of 
working. 
