292 The American Geologist. Mays 0 
ious genera have been derived, through changes affecting any or 
all the lobes. The modifications usually consist in the pro- 
gressive absolescence of the anterior annulations, finally pro- 
ducing a smooth glabella, as in //laenus and Niobe. The neck 
segment is the most persistent of all, and is rarely obscured. 
The third, or mandibular segment is frequently marked by 
two entirely separate lateral lobes, as in Acidaspis, Conolichas, 
Chasmops, etc. Likewise, the fourth annulation carrying the 
first pair of maxillz is often similarily modified in the same 
genera, also in all the Protide, and in Cheirurus, Crotaceph- 
alus, Sphaerexochus, Ampyx, Harpes, etc. Here again among 
adult forms, the stages of progressive differentiation may be 
taken as indicating the relative rank of the genera.” 
We are certainly presented here with a regulated and fairly 
evenly graded development which seems independent of ex 
ternal accidents, contingent on variable disturbances, as nat- 
ural selection or survival, and are forced to contemplate a 
series of physiological phenomena which possesses the fixity of 
an undeviating tendency. It is probable that an evolutional 
process started, it advances with certainty, with or without 
reinforcement from environment. 
What has been called the “biogenetic law” has been illus- 
trated also in cephalopods and the Pelecypoda, and as Mr. 
James Perrine Smith has remarked “paleontology is synony- 
mous with phylogeny;’’ it is a record in fossils of changes ’ 
which bring about determinative results, and the scheme it 
presents seems to have a. systematic effectiveness which lies 
outside of the fortuity. of selection or environment. 
An examination of the succession of changes which have 
produced the modifications in form or structure in the Brach- 
iopoda, trilobites, Pelecypoda and cephalopods, accentuates the 
general impression that while selection, environment, survival, 
etc., have played a part in the influences that have shaped this 
succession, there is a different and mandatcry law behind them 
which absolutely, without their secondary intervention, would 
have produced a very similar result. 
In the development of form in the Brachiopoda we find 
that morphologists dwell upon the shortening of the pedicle 
and the tendency, thus started, of widening the shell as the 
posterior part of the shell is brought nearer to the object of 
