NOMENCLATUBE OF BTAGES OF OBOWTB AM' DECLINE 17 



all other forms, especially in the devonian i gustisellnte 



embryos, the tendency I i and to inherit the depressed 



primary radical whorl of Anarcestes, produced the Goniatitinula, and affected 

 even the protoconch. The protoconoh through heredity becomes depressed fusi- 

 form by lateral expansion in the a llati, and the embryonic nautiloid 

 character of the first septum in the asellate forms and its tendency to form 

 nd ventral saddle in the latisellate and a narrow ventral saddle in the 

 elative with tin* progression of form. 

 mil. i is :i true larva, corresponding to adults within the order. 

 • the term because it is the characteristic larval form of the Ammonoidea, 

 which was introduced at first among adult Goniatitinm, and in the higher forms 

 of this group became, by acceleration, fused with the microsiphonula. 



o Branco enable us to Btate that this pro 

 sion in complication of the embryo in form and Butures has no counterpart 

 in the pai iriea of adult shells, except among 



Nautil lently the angustisellate peculiarities of the ventral Baddies 



and d< haracteristic of the latisellate and angustisellate em- 



it • l» . dan and Trias were not due to inheritance from primitive 

 adult later modifications originating in the caecosiphonula 



ling. They were correlative with the earlier or accelerated 

 the depressed whorl, and the quicker growth in bulk of the 

 whorl. Similar tendencies hive been observed repeatedly in different pn 



itiloidea. Thus, wherever we have been able lo trace the series 

 loose-coiled, to a close-coiled nautilinn form, this 

 rule has more complicated suture-;. The universal result of such pro 



ilization among the adult forms of Nautiloids is closer coiling, due to 

 quicker growth in hulk of the whorl, and is accompanied also by the evolution 

 of a Is saddle. It is not surprising that similar mechanical results 



should follow in the septa of the embryos of Ammonoidea, when similar cl 



rred through the ae.-. -l. -rated inheritance of the 



il whorl, and closer coiling in the csecosiphonula. 



the shortening of the larval stages in the Latisellati 



ipared with t In- Asellati, and the still greater acceleration of development 



ring in the Angustiw llati, and the correlation of these with the general pro- 



the adults of the sai livisiona in time 



I confirms o ously published opinion- of the relation of embryos 



lults, and with those here published regarding the inheritance 



of the primary, radical, smooth form in the depressed embryos of Latisellati and 

 \ rrelative evolution of the sutures and coiling 



The microsiphonula appeared in the Ammonoidea with the second septum, 

 in what i- morphological \\ the second air-chamber when compared with Nauti- 

 • tall) the in the- apex of tb< 



i form, -nee the siphon b< ■ > j rapidly 



i lion among 



the i \ not formed until later, though the pre< 



