FEBRUARY 8, 1884. | 
logical and generalized picture of exact corre- 
spondence between all the changes in the life 
of a nautilian close-coiled shell and the life of 
its own group accord with the facts, we must 
be careful to limit it to groups quickly evolved, 
and these exclusively paleozoic. 
In 1843 Auguste Quenstedt began re- 
searches which ought long ago to have led to 
this solution. He demonstrated by repeated 
examples, that among diseased types the most 
extensive changes of form and structure might 
take place in a single species, and within the 
narrowest limits of time and surface-distribu- 
tion. Quenstedt was thus the first to show 
that in diseased forms the shell had the in- 
herent habit of reversing the process of growth 
and evolution, and of becoming more and 
more uncoiled by successive retrograde steps. 
Von Buch and Quenstedt, master and disciple, 
and the author independently of either of these 
predecessors, in three successive researches, 
have arrived at the identical conclusion, that 
these uncoiled shells are truly distorted, or, as 
we may more accurately express it, pathologi- 
cal forms. They are not, however, rare or 
exceptional, as one might at first suppose, but 
occur in numbers and in every grade, — from 
those that differ but little from the normal 
forms, to those that differ greatly ; from those 
that are exceedingly confined in distribution, 
to those which lived through greater lengths 
of time. But in all cases they exhibit degra- 
dation, and are expiring types. The author 
has repeatedly traced series of them, and stud- 
ied their young, partly in Quenstedt’s own col- 
lection. In all cases they show us that great 
changes of form and structure may take place 
suddenly; and this lesson could have been 
learned from Quenstedt’s work and example 
as well forty years since as now: and in all 
species the young are close-coiled, even in 
some which are arcuate in the later larval, 
adolescent, and adult stages. Baculites, the 
extreme form, is straight, and the young still 
unknown. 
When we attempt to resolve these pathologi- 
cal uncoiled series and forms, which show by 
their close-coiled young that they were de- 
scended from close-coiled shells, we find our- 
selves without comparisons or standards in the 
early life of the individual. The laws of gera- 
tology —that the old age of the individual 
shows degradation in the same direction as, 
and with similar changes to, those which take 
place in successive species or groups of any 
affiliated pathological series of uncoiled and de- 
graded forms —here come into use, and serve 
to explain the phenomena. This correspond- 
SCIENCE. 
147 
ence is shown in the uncoiling of the whorls, 
loss of size, the succession in which the orna- 
ments and parts are resorbed or lost, the ap- 
proximations of the septa, and position of the 
siphon. It is quite true, as first stated by 
Quenstedt and also by D’Orbigny, that every 
shell, when outgrown, shows its approaching 
death in the close approximation of the last 
sutures, the smoothness of the shell, the de- 
crease in size, etc.; but, in order to realize 
that these transformations mean the same thing 
as those which take place in any series of truly 
pathological forms, we have to return to the 
types in which unfavorable surroundings have 
produced distortions or effects akin to what 
physicians would term pathological. ‘This fre- 
quently happens in small series of Nautiloidea ; 
and, if we confine ourselves to these, we can 
make very accurate comparisons: or, on the 
other hand, in the case of the Ammonoidea, 
we may trace the death of an entire order, 
and show that it takes place in accordance 
with the laws of geratology. Such series, 
among the Nautiloidea, are abundant in the 
earlier formations ; but they have not the gen- 
eral significance of the similar forms among 
the Ammonoidea, and can be neglected in this 
article. There are no known cases of degraded 
series of uncoiled forms among the ammonoids 
of the earlier or paleozoic periods: they may 
have occurred, but they must have been ex- 
cessively rare. In the trias and early Jura, 
pathological uncoiled forms are rare among am- 
monoids, but in the middle and upper Jura they 
increase largely ; and finally, in the upper cre- 
taceous they outnumber the normal involute 
shells, and the whole order ceases to exist. 
Neumayer has shown, that a similar degrada- 
tion occurs in all of the normal ammonoids of 
the cretaceous, and that their sutures are less 
complicated than those of their immediate an- 
cestors in the Jura. This proves conclusively, 
that the degradation was general, and affected 
all forms of Ammonoidea at this time ; since the 
uncoiled forms are not confined to special local- 
ities, asin the Jura, but are found in all faunas 
so far as known. The facts show that some 
general physical cause acted simultaneously, 
or nearly so, over the whole of the known area 
of the world during the cretaceous period, 
and produced precisely similar effects upon the 
whole type as had here and there been notice- 
able only within limited localities and upon 
single species or small numbers of species dur- 
ing the previous periods. This general cause, 
whatever it may have been, acted on the type 
so as to cause the successive generations of the 
larger part of the shells to become distorted 
