50 
ANNALS NEW YORK ACADEMY OF SCIENCES 
also remembered that the life of any individual is a compressed and ab¬ 
breviated edition of the life of the race and that in any natural classification 
the individual must be the unit of comparison, it will be possible to trace 
out the relationship and stages of development of any group, provided enough 
of the structure is preserved to show what the development of the individual 
has been. 
Few groups lend themselves better to studies of this kind than the family 
Zaphrentidse of the rugose corals. This is a family of wide geographical 
distribution and occurs throughout deposits accumulated through long 
periods of geological time. In the majority of the genera and species, the 
individuals are solitary and have grown in free and open space and are not 
marred or distorted by crowding or the presence of other forms. The nature 
of the coral skeleton is such that all stages of development are recorded 
from the time the little polyp embryo secrets its first calcareous support till 
the polyp finally dies and its full-grown calyx or cup becomes buried in the 
surrounding mud. Many of the fossil corallites are so perfectly preserved 
that even the youngest stages can be found and studied, and it is upon studies 
of this nature that the following paper is based. 
In the course of these studies, three methods of treating the material 
were pursued, according to its nature and abundance, the method of 
fossilization and the object in view in studying the particular specimen: 
1. Treating with acid. — Silicified specimens in a calcareous or lime¬ 
stone matrix were treated with acid. This method was particularly useful 
in preparing the specimens of Streptelasma profundum from the Black River 
and Trenton limestones. 
2. The making of microscopic sections through the corallite. — In the 
course of these studies many microscopic sections of corals were cut. This 
method furnished a permanent record of all stages observed, but it was 
impossible to cut the sections thin enough to preserve all the stages in 
development. Sections of the earliest stages were extremely difficult to 
make, and even when made could rarely be ground thin enough to show 
anything distinctly. 
3. Grinding from the tip of the corallite and observing and sketching 
each successive step in development. 1 This proved to be the most satisfactory 
method of following the developmental stages. Its great drawback lies in 
the fact that each stage must be destroyed before the next stage can be seen, 
the only permanent records being the sketches made and observations noted 
during the grinding. 
1 This method was first described in print by Duerden, but it was used by the author 
before Duerden’s publication. 
