ete E ’s OOTO) ly ee S 
_ phology, or what used to be called comparative 
154 Recent Literature. [February, 
“In some of them, certainly, it is not an over-statement to say 
that the chronology of the evolution of form, the development of 
the individual, the gradations in the adults and the general differ- 
ential characteristics all tell the same story, and are decisive for 
the opinion that in all the larger series of shell-bearing Cephalo- 
poda, the nautilian shells belong to several distinct series and 
arose independently from straight cones through the intermedium 
of a graded series of arcuate and gyroceran or closely coiled 
forms. The generic terms, Cyrtoceras, Gyroceras and Nautilus 
are really only descriptive terms for the different stages in the 
development of an individual, and also the different stages in the 
development or evolution of the series of adult forms in time. 
In other words, each of these genera as now used, include repre- 
sentatives of all the different genetic series of Tetrabranchs, 
which are either young shells in the corresponding stage of 
growth, or adult shells in the corresponding stage of evolution.” 
Professor Hyatt maintains that the Nautilini were derived 
directly and independently from a straight cone, and that this 
primitive nautiline form was a close ally and ancestor of the 
straight orthoceran-like Bactrites of the Silurian. “ All the re- 
maining ammonoids are more concentrated in development, and 
skip the orthoceran, cyrtoceran and gyroceran stages of their evo- 
lution in time. They are evidently descendants of the close- 
coiled Nautilinidz, and the evidence here is very strong that the 
whole order.of Ammonoideaarose from a single organic center 
of distribution, the Nautilini of the Silurian. The succession in 
time, the evidence of gradation in structure and the development 
exactly accord with this statement. Nautilinidz, Goniatites, Tri- 
assic transition forms of Ammonitinz and the true Ammonites of 
the Jura form a perfect progessive series.” 
During the investigation Professor Hyatt has been able to add 
to the facts he has already brought forward in support of the law 
_ of acceleration, though he now prefers to designate it as “the 
law of concentration of development.” All the more generalized 
or lower types, he says, have a direct mode of development, and 
the more specialized or complicated progressive types have, when 
at the acme of their development, a more indirect mode of devel- 
opment.” The types which are descended from these last have 
often a mode of development which in many forms is an appa- 
rent return to the direct mode of development again.” 
It is impossible to farther epitomize this important paper, and 
we shall look forward with much interest to the complete illus- 
trated memoir. "aa o ) 
ARKER 
of animal mor- 
anatomy, lies at 
> OIA course of Instruction in Zostomy (Vertebrata). By T. Tarver. 
"With a illustrations," London, Macmillan & Con 1884. 2m, pp. sey, ene 
FT A eee TT I oa w 4 
Ly Xe 
