396 
epinepionic periods of development in obedience to the law of the 
cycle does not carry the structure back with it to a repetitjon of the 
orthoceran siphuncle and sutures. 
The structure of an individual during its development might be 
represented graphically by an irregular spiral of one incomplete 
revolution which describes a curve, continually increasing its dis- 
tance from the point of departure until the meridian of the ephebic 
stage is reached, and then beginning to return. Sucha curve would 
always as a spiral rise more or less vertically, and consequently, 
even if it completed the revolution, must terminate in space. It 
might, perhaps, reach nearly to the same imaginary vertical plane, 
but never to any point approximate to that of its departure. Structure 
separates the extremes of life as widely as possible, and does not 
permit us to regard them as approximate, nor can one regard old 
age, however complete its return in external form, as a reversion. 
One of the most noteworthy contributions of bioplastology is 
that it gives proper values to this class of analogies and shows them 
to be constantly recurring in the individual and in the phylum in 
obedience to well-ascertained laws of morphogenesis. 
The different stages have been described by Dr. Beecher among 
Brachiopoda, Dr. Jackson among Pelecypoda, and the author 
among Cephalopoda; and Buckman and Bather and also Blake * in 
England, and Wiirtenberger in Germany have admitted their exist- 
ence, and the last redescribed them. Wiirtenberger has admirably 
described the phenomena of bioplastology as they occur among 
Ammonitine, and correctly interpreted the law of tachygenesis and 
its action in these forms, but failed to quote either Prof. Cope or 
the author. ‘This omission was not so remarkable as the fact that 
Neumayr and some other investigators, after they had received the 
printed records of the work done in the same direction in this 
country, continued to quote Wiirtenberger as the sole discoverer of 
these phenomena and of the law of tachygenesis. Wiirtenberger’s 
work was apparently independent, and it has higher value on that 
account, but it needs rectification from a historical point of view. 
Buckman and Bather propose to use the prefix ‘‘ phyl’’ for forms 
occurring in the phylum which represent in their adult characters 
stages in the evolution of the phylum corresponding with those in 
the development of the ontogeny, and give an instructive table in 
* “ Byolution and Classification of Cephalopoda,” Proc. Geol. Assoc. Lond., Vol. xii, pp. 
276-295, 1892. 
