1893-] 95 [Hyatt. 
otlier the termination of ontogenesis. Departing from the 
ephebic period in either direction towards these extremes one 
finds the same hxw. Contiguous stages of development^ lohen con- 
sidered in sequence, differ less from each other arid from the adult 
the nearer they are to the ephebic jjeriod, and they differ on the other 
hand more from the adidt and from, each other in structure and 
form the nearer they are to the t7no extremes of the ontogeny. This 
is an evident coroUary from tl>e phenomena of the ontogenetic 
cycle and need not be dwelt upon here. It is cited only to show 
that the differences between the nepionic, neanic, and ephebic 
stages are less noticeable than those of the embryonic and nepionic 
or the epliebic and gerontic, and this explains wliy I did not snb- 
divide the intermediate stages in 1888 as I then did the embryonic 
and the senile. 
1 now propose the following nomenclatnre whicli iloes, it is 
hoped, fuller justice to every stage. ^ 
The terminology of the different branches of research which 
come properly under the head of bioplastology is recognized at 
present only in the case of embryology, but it is obvious to the 
student of epembryouic development that similar terms for the 
study of other stages and periods will in course of time be needed, 
and in fact the old terms, nealogy, ephebology, and geratology, 
are cited in that sense in the Century dictionary, and may intro- 
duce some confusion. It is not now necessary to discuss this 
question but only to draw attention to the facts. I therefore pass 
on to the consideration of the term epembryonic. 
Among fossil nautiloids it is rarely practicable, on account of 
the frequent destruction of the protoconch, to find an embryonic 
stage. My last work on Carboniferous cephalopods contains 
descriptions of the entire ontogeny of a number of species with 
the exception of the embryonic stages. In such cases the fact 
that the embryology is wholly omitted can be pointed out by the 
1 It is my grateful duty to add that I have had the unremitting help of Dr. C. E. 
Beecher, and have consulted with Dr. R. T.Jackson of Cambridge, and Mr. J.M.Clarke 
of Albany, and also with Mr. Buckman, and I wish to express to these gentlemen my 
indebtedness for suggestions and advice of essential importance. Exce})t in the reten- 
tion of one term, "nepionic," the nomenclature is more theirs than mine. I also desire 
to thank Professor Reynolds of New Haven and Prof. William W. Goodwin of Cam- 
bridge for the earnest help they contributed to the formation of a table which, for 
reasons given above, was not used, as well as for advice which influenced the framing 
of the one finally adopted. 
