REVIEWS AND BOOK NOTICES. 
Tar Empryorocy or Fosstr CerHatorops.*—This essay con- 
tains some of the results of several years’ study of the rich collec- 
tion of fossil Cephalopods contained in the Cambridge museum. j 
The special investigations recorded here were made for the purpose 
of ascertaining the limits of the embryological period among the 
typical Ammonites. In order to do this the author made sections ; 
of the shell and worked out the form of the embryo or young ani- 4 
mal just after being hatched. This may be detected by breaking 
away the older whorls, and getting at the minute globular sac, 
which represents the shell in its first stage. This sac may be 
found in Ammonites and Goniatites, but in the shell of Nautilus it 
is not retained, though ‘traces of its former existence are appar- 
ent on the apex of the first whorl in the form of a scar or cicatrix. 
Into this sac opens the first whorl of the shell; other whorls are 
added, until they form a long series coiled up closely, as in the 
Ammonites so familiar to geological students.” As is well known 
to palzontologists there are all grades of form from the “ straight 
Orthoceras to the coiled Nautilus, and inversely, among Ammo- 
_ noids from the closely coiled Goniatites and Ammonites to the 
straight Baculites; the general morphology being readily and ac- . 
eurately expressed as a coiling up of a straight cone, and the 
subsequent uncoiling of the same at later stages of the earth’s 
history. The shells are almost universally classified in accordance 
with this coiling and uncoiling, with which also the structure of 
the siphon and septa are more or less correlated.” Prof. Hyatt 
SEERE a VR ge en ay eee 
SD Ane 210 Sa a ee N, 
has endeavored, and we think with great success, to show that this 
series of forms is epitomized in the life of the individual Nautilus - 
or Ammonite. The young in these Cephalopods are at first un- 
coiled like some genera, and the different degrees of coiling up find 
a permanent expression in the genera of Ammonoids. 
He figures the embryos of certain Goniatites, and from the dif- 
ferences presented by them, a succession of forms is detected which 
_ accords with what we know of the morphology of these P 
_ pods and their geological succession. He concludes that — ` 
=- * Fossil Cephalopods of the biures or Cemparative Zoology; Embryology. By 
Ion Alpheus Hyatt. (Bulletin of the Mu , Cambridge. Mass., 
z vol. iii, No. 5. Cambridge, 1872. 8vo. pp. 116, with cuts and four lithographic , plates.) 
s 04) 
