Fespruary 8, 1884.] 
the individual. We can accurately compare 
the rise and fall of the individual and its whole 
eyele of transformations with that of any of 
the single series or branches of the same stock 
which become highly specialized and then de- 
generated ; but, when we attempt to go farther, 
we meet with similar difficulties to those en- 
countered in tracing the progress of types and 
orders. The radical and persistent types are 
still present, and teach us, that, as long as they 
exist sufficiently unchanged, new types are a 
possibility. We have traced many of these 
in the two orders, and have found that they 
change and become more complicated, and that 
probably a purely persistent or entirely unpro- 
gressive type does not exist among the fossil 
Cephalopoda. The most celebrated example 
of unchanging persistency has been, and is now 
supposed to be, the modern Nautilus. We 
think, however, that when our observations 
are fully published, it will become evident that 
the similarities of this shell to some of the 
Cambrian coiled forms — which have caused 
Barrande and others to suppose that it might 
be transferred to the Cambrian fauna without 
creating confusion — belong to the category 
known to the naturalist as representation ; that 
is, similarities of form, and even of structure, 
in the adults, but with young having entirely 
distinct earlier stages of development, and 
belonging to distinct genetic series. Still, com- 
parative unprogression or persistency is com- 
mon in all radicals; and they force us to 
recognize the fact, that the orders could have 
produced new series, perhaps even in the cre- 
taceous, if it had not been for the direct un- 
favorable action of the physical changes which 
then took place, so far as we now know, over 
the whole earth. 
Thus, in making our comparisons between 
the life of the individual and the life of the 
group, we cannot say that the causes which 
produced old age and those which in time pro- 
duced retrogressive types were identical: we 
can only say, that they produced similar effects 
in changing the structures of the individual 
and of the progressive types, and were there- 
fore unfavorable to the farther development 
and complication of these types. In their ef- 
fects they were certainly similar; but in them- 
selves they might have been, and probably 
were, quite different, agreeing only in belong- 
ing to that class of causes which we distin- 
guish as pathological, or those whose nature 
can be generally summed up as essentially 
unfavorable to the progress, and even to the 
existence, of the organization. 
In order to understand the meaning of these 
SCIENCE. 
149 
evidently degraded structures, we must turn 
back to our first remarks upon the order. The 
apertures and forms of the retrogressive shells 
all show that they were exceptional, that they 
had neither well-developed arms for crawling 
nor powerful pipes for swimming; that, in 
other words, they could not have carried their 
spires in any of the ordinary ways. Their 
habitats, therefore, must have been more or 
less sedentary ; and like the sedentary Gastro- 
poda, as compared with the locomotive forms, 
they presented degeneration of the form and 
structure of their higher and more complicated 
ancestors. ‘Their habitats did not require the 
progressive grades of structure, and they dis- 
pensed with or lost them; and in many cases 
this took place very rapidly. This retrogres- 
sion was in itself unfavorable to a prolonged 
existence ; and the geratologous nature of the 
changes tells the same story, so that we can 
attribute their extinction to the unfavorable 
nature of their new habitats, and also call them 
pathological types without fear of misrepresent- 
ing their true relations to other forms. 
We have necessarily avoided even allusions 
to some of the most important confirmatory 
facts; but we hope our effort will at least 
show that the theory advanced is a reasonable 
one, and that the fossil Cephalopoda are worthy 
of the attention of even the most enthusiastic 
of the young disciples of the modern school of 
embryology. The theories of this school will 
have to stand tests of which they have now not 
even a faint idea, and it is to be hoped they 
will not long neglect the precaution of know- 
ing also the past history of the types they 
often so incautiously and confidently handle. 
ALpHEus Hyatt. 
THE MOTION OF WAVES OF COLD IN 
EE WOUNT TED 3S TA TES. 
Tue chief signal-officer of the army desiring 
to learn the progress of waves of cold across 
the United States, an investigation has been 
undertaken in order to determine the appear- 
ance of such waves, their approximate velocity, 
and general line of advance. It would seem, 
at first sight, as though the problem might be 
solved by drawing isotherms (i.e., lines through 
points at the same temperature) on consecutive 
days, from simultaneous observations over the 
whole country. If, then, there were a progres- 
sive motion, the study of these lines would 
show it. It has been found, however, that a 
cold wave does not travel in a well-defined 
closed curve ; and, more than that, the gradual 
increase of temperature, as the curves approach 
