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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 

 stage. 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 Organism en, 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. 



