:i:n. LATURE OB Bl kGES OF GROW I'll \M> DEC! IM 16 



point to make in its favor. If the protoconch of Nautiloids was an empty eon- 

 chiolin shell itiid represented the veliger Btage, it most certainly could nol have 

 tral form from which the calcareous tendency of the same Btage in 

 Ammonoids was derived. The characteristics of the asiphonula of Nautiloids arc 

 however, j u-t what are needed i<> till the lm|>. The apes at this stage in Nau- 

 tiloids is rounded and calcareous. The tendency to deposit calcareous matter 

 could therefore have been inli»-i-tt»-«I from an ancestor corresponding to the asi- 

 phonula, and which we will name the Asfphonophora, The Asiphonopbora must 

 have bad a calcareous shell acquired as an adaptive character, without internal 

 or i Biphon. This form could not have been l>\ any means bo 

 moved from the ancestor of the veliger as the immediately following an- 

 isiphonula, which we have named the Macrosiphonopliora 

 This must have bad septa and a central axis of cseca, or at any rate at least 



in and a e;ceum. 



Tlic characters of the Asiphonophora, when transmitted to the Ammonoids 

 _ to tii.- law of acceleration, would bave been inherited earlier than in 

 Nautili ire bave affected the growth of tin- protoconch, ami 



would lia\ ily produced tin- calcified Bhell of this -ta_ r >' in Ammonoids 



The fusion of the protoconch with tin' conch in all Ammonoids was the imme- 

 resull of this process, and in this way tin- more tubular form and freer 

 connection of the protoconch with tin- tin.- conch, and the constant adhesion 

 of tin- former to the latter, ran be explained. 



The disappearance of tin- asiphonula as a distinct Btage in the young of 



the Ammonoids appears to us, therefore, not an argument against the deriva- 



of the Ammonoids : \ bonophora, but in favor of this opinion. In 



ii* to us that, in order to disprove it, opponents will have to find 



•rix upon the apex of the protoconch in the Ammonoidea. According to 



the uncompromising attitude of those who iu^i-t upon the naked facts, and are 



ns, the protoconcb is the apex of the conch in Ammonoids, 



and t :i\ cicatrix upon the tip of this is a difficulty they can only 



surmount b that I neral and speciul homologies we bave traced, 



and all the einbryological ami na?| is, are purel) homoplastic, 



ami do not indicate the derivation of the Ammonoids from any form of Nauti- 



i must al-o explain away the similarity of the | oconch in external 



-hell in Gasteropoda, since this i^ an earlier Btage than 

 k of the true concb in Nautiloids, Ammonoids, and all cephalous 



mollusks. Can any of th gentlemen tell us why the cicatrix does n o( appear 



upon the protoconch of Ammonoids, and explain at the same ti how that 



■bell came to be similar to the \. .1 in the Cepbalophorous Molluscs 



on the one hand, ami th.' apex of the conch of Nautilus on tl ther'.' 



I- ; Iso, that we do not insist that the primary radical of 



th-- Ammi nded dii ectl) from End< i 



but that it bad probably come from a prototype 1 i K «• the veliger, possibly, as 



!\ represented l>\ the genus Dentahum. 

 The n to our translation of the < . must have been 



