— 
to 
REVIEWS AND BOOK NOTICES. 107 
Orthoceratitic young of Goniatites fecundus. This happens occa- 
sionally in the lower Jura, and finally, after the progressive stage 
of the whole order ‘passes its climax, in the lower and middle Jura, 
we find the development of a whole group affected by ay retarda- 
tion, and the spiral is common to several generic form 
We believe that the author is on a line of on bearing 
most intimately not only on the origin of organic forms, but also 
on a question next in importance, the law of their extinction. How 
an animal or plant is produced is a matter of the greatest interest, 
but is not the cause of its decay and death one almost as interest- 
ing? 
Since the present essay was published the author has gone to 
Germany to study the collections of fossil Cephalopods in the 
museums of Hanover, Stuttgart, Tubingen, etc. From a recent 
letter we take the liberty of quoting some remarks which confirm 
the conclusions of his first paper on this subject,* and of the trea- 
tise before us. 
He took as a test of the whole order the family of Arietide, 
which are confined to one formation, the lower Lias. 
“ It is simply wonderful to see how perfectly the geological 
position of each species in the formations here agrees with its place 
in the series as determined by ee The successive 
minor formations of the lower Lias nothing more ‘ink succes- 
sive faunæ. They are the smallest divisioils that it is possible to 
make in the geological series of rocks, an | yet t there is no more 
confusion than results paed one species passin. 
y another, or living lon Chines bed ak 
Thus @ may live ligir than b and appear a 
ilougaide of it, but the young of b is pe ae TEE oe 
adult of a a always. Now, then, I think we can 
depend upon development to give us the Sek of descent, and 
not only that tg more. In fact I feel sure that I can give 
the reason why one entire fauna is different from the next, ve! 
that which sens ‘it and why also the species on the sam 
level have some common characteristics. This is the jepitiinate 
>~ 
8 
_ *On is Parallelism between the different Stages of Life in the Individual, and those 
in the entire group of the Molluscous order f the B a 
Society of 3 Natural History’ Vol. 1. Part 2. 1867). The characteristics of the ‘period of a 
epli idea pi 
is extended t by Hyatt to include the coll life of this order the class of Cephisle: 
pods Tori th | int Sctence culminated, 
and then declined and wont out in forms both reminding us of the embryos of the 
Nautilus and Ammonite, as well as the earliest generic forms of the order. Thus ac- 
cording to Hyatt’s theory the anerest stages of the life of the individual Nautilus or 
tes accord with those of the collective life of the entire order. 
