No. I.] LARVAL STAGES OF SCHLOENBACHIA. 243 



changes from the larval period up to maturity. But the higher 

 Devonian and Carboniferous forms go through several generic 

 changes before they reach maturity, while Mesozoic genera 

 have still longer larval and adolescent periods, — that is, longer 

 in the sense of going through more stages. In Paleozoic spe- 

 cies, however, one rarely finds ammonoids preserved so that the 

 inner coils may be separated. In Mesozoic species, while the 

 preservation is often good, the acceleration is usually so great 

 that any certain interpretation of the meaning of larval stages 

 is difficult, not to say impossible. 



Method of phylogenic resemxh. — Since ammonites preserve 

 in each individual a complete record of their ontogeny, one 

 might work out the life history of each species from a single 

 specimen by making drawings of each stage before pulling off 

 the coils representing this stage. In some few cases the writer 

 has succeeded in taking off the outer coils so as to show almost 

 the complete ontogeny in a single specimen without destroying 

 the specimen. But this method usually necessitates the destruc- 

 tion of those parts that are taken off, and so the original is 

 lost, and the naturalist has to show for his work only his notes 

 and drawings, which may or may not be sufficiently accurate ; 

 his results cannot be verified. 



The more satisfactory way is to select a number of well-pre- 

 served adults, so as to be sure of the identification of the species 

 and to break off the outer coils until the desired stages are 

 reached. To do this, finger nails and steel dental chisels are 

 all the tools needed. After the specimen is reduced to a small 

 size the coils are pulled off under water to prevent loss. The 

 material used must be selected with great care, preferably lime- 

 stone, not so soft as to crumble nor so hard as to shatter.^ The 

 young ammonite may be studied under the microscope in three 

 different mountings : dry on white cardboard to see the surface 

 markings; on white cardboard in a drop of water to see the 

 septa and shape ; under water in a watch-glass over a strong 



1 The results given in this paper are based on the study of about 150 specimens, 

 illustrating all the life history of Schloenbachia oregonensis, but of course these 

 could not all be figured, nor even included in the tables. Only the distinct stages 

 and not the transitions were selected for illustration. 



