864 THE JOURNAL OF GEOLOGY. 
in much earlier ontogenetic stages. The degeneration is exhibited by 
ia reversion to earlier characteristics. ‘The shell becomes straightened, 
looses its ornamentation and the sutures become more simple, but in 
all cases it can be shown from a study of the younger ontogenetic 
stages, that these degenerate forms spring from a closely coiled radical 
stock. In no case do retrogressive series give rise to secondary radi- 
cals which originate new series. 
The second chapter is devoted to “ Principles of Bioplastology,” 
or the study of the correlation of ontogeny and philogeny. The chapter 
is made up largely of the explanation of technical terms. Five onto- 
genetic stages are recognized: (1) embryonic, (2) nepionic, (3) neanic, 
(4) ephebic, (5) gerontic. Each of these, except the embryonic, is 
divided into three substages the names of which are formed by the use 
of the prefixes ana, mefa and para, as ananepionic, metanepionic and 
paranepionic. The corresponding phylogentic stages are designated 
iby the use of the prefix pxylo, as phylonepionic, etc. 
The general adoption of a series of exact terms in investigations of 
this nature is a necessity, and no one is better fitted to propose these 
terms than Professor Hyatt. It is desirable that other investigators, 
as some have already done, should adopt this system of nomenclature. 
Chapter III. is devoted to the discussion of the ontogenetic stages 
of the nautiloidea and ammonoidea. From direct observations Pro- - 
fessor Hyatt has determined “‘¢hat the substages of development in ontog- 
eny are the bearers of distal ancestral characters in inverse proportion 
and of proximal ancestral characters tn direct proportion to their removal 
an time and position from the protocouch or last embryonic substage.” 
As a general rule the nepionic stage of nautiloidea draws to a close 
and the neanic characteristics begin to appear, at or near the comple- 
tion of the first volution, which growth brings the whorl in contact 
with the apex or dorsal side of the couch. The ananeanic substage is 
marked by the first. appearance of the impressed zone. This is the 
mame given to the area on the dorsum affected by the contact of the 
dorsum of the growing whorl with the venter of the already formed 
whorl of the next inner volution. 
This impressed zone can be readily seen to be at first due entirely 
to a mechanical cause, the resistance of the inner volution to the 
growing shell of the outer. It is the acquired character the phylogeny 
of which the author discusses in detail. It can be shown that the 
impressed zone is invariably consequent upon close coiling, as it is 
never found in adults of any ancient and normally uncoiled shells. 
