392 
two extremes of the ontogeny. This is an evident corollary from 
the phenomena of the ontogenetic cycle and need not be dwelt 
upon here. 
The terminology of the different departments 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 epembryonic 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 introduce 
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 ~ 
stagé. My last work on Carboniferous cephalopods contains descrip- 
tions 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 use of the 
term ‘‘epembryonic stages,’’ and this has already been found use- 
ful above. It only remains to add that the same prefix is also useful 
in designating the exclusion of other stages—thus one can speak 
also of the ‘‘epinepionic’’ or ‘‘epineanic’’ stages in this same 
way without danger of confusion with any other term.* 
It is often possible to employ a more specific and characteristic 
designation than epembryonic. Thus among shell-bearing forms 
one can distinguish between the embryonic shell and the true shell ; 
for example, the protegulum and tegulum of Brachiopoda as defined 
by Beecher, the prodissoconch and the dissoconch of Pelecypoda as 
defined by Jackson, the periconch and conch of Scaphopoda, the 
protoconch and conch of Cephalopoda. In all of these forms it is 
practicable to speak of tegular, dissoconchial, or conchial stages or 
periods, meaning thereby all of the epembryonic stages of these 
types. 
Haeckel, in his Morphologie der Organismen, sketched the physi- 
ology of ontogeny and phylogeny and gave the general correlations 
of the two series of phenomena, together with an appropriate 
* Postembryonic is in use for the young stages among embryologists, and is equivalent 
to the term nepionic, but it is not consistent with the other terms of bioplastology, and 
is a hybrid. 
