NOMENCLATURE OF STAGES OF GROWTH AND DECLINE. a7 
all other forms, especially in the devonian latisellate and triassic angustisellate 
embryos, the tendency to become closely coiled, and to inherit the depressed 
primary radical whorl of Anarcestes, produced the Goniatitinula, and affected 
even the protoconch. ‘The protoconch through heredity becomes depressed fusi- 
form by lateral expansion in the Angustisellati, and the embryonic nautiloid 
character of the first septum in the asellate forms and its tendency to form 
a broad ventral saddle in the latisellate and a narrow ventral saddle in the 
angustisellate embryo is correlative with this progression of form. 
The goniatitinula is a true larva, corresponding to adults within the order. 
We use the term because it is the characteristic larval form: of the Ammonoidea, 
which was introduced at first among adult Goniatitinez, and in the higher forms 
of this group became, by acceleration, fused with the microsiphonula. 
The remarkable researches of Branco enable us to state that this progres- 
sion in complication of the embryo in form and sutures has no counterpart 
in the parallel series of any pre-existing series of adult shells, except among 
Nautiloidea ; consequently the angustisellate peculiarities of the ventral saddles 
and deep lateral lobes characteristic of the latisellate and angustisellate em- 
bryos of the Devonian and Trias were not due to inheritance from primitive 
adult radicals, but were later modifications originating in the cacosiphonula 
from close coiling. They -were correlative with the earlier or accelerated 
development of the depressed whorl, and the quicker growth in bulk of the 
whorl. Similar tendencies have been observed repeatedly in different progres- 
sive series of Nautiloidea. Thus, wherever we have been able to trace the series 
of species from a straight, or loose-coiled, to a close-coiled nautilian form, this 
as a rule has more complicated sutures. The universal result of such progres- 
sive specialization among the adult forms of Nautiloids is closer coiling, due to 
quicker growth in bulk of the whorl, and is accompanied also by the evolution 
of a larger ventral saddle. It is not surprising that similar mechanical results 
should follow in the septa of the embryos of Ammonoidea, when similar changes 
in the mode of growth occurred through the accelerated inheritance of the 
depressed anarcestian radical whorl, and closer coiling in the ceecosiphonula. 
Branco has observed the shortening of the larval stages in the Latisellati 
as compared with the Asellati, and the still greater acceleration of development 
occurring in the Angustisellati, and the correlation of these with the general pro- 
gress in complication of the sutures of the adults of the same divisions in time. 
This confirms our previously published opinions of the relation of embryos 
and adults, and also agrees with those here published regarding the inheritance 
of the primary, radical, smooth form in the depressed embryos of Latisellati and 
Angustisellati, and the correlative evolution of the sutures and coiling. 
The microsiphonula appeared in the Ammonoidea with the second septum, 
in what is morphologically the second air-chamber when compared with Nauti- 
lus, though actually the first existing in the apex of the true conch. This 
microsiphonula is also an accelerated form, since the siphon becomes very rapidly 
or even abruptly attenuated. The collar or distinctive organ of the siphon among 
the normal Ammonoids was not formed until later, though the precise period 
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