i \ i i i;\ \ i. ii i.i.i.. 



M. Mnnicr-rhalmas has recenlh ende;i \ mvd to prove tli:it the 

 Ammonites are not tcl r: branchiate CCphaJopoda, allied '< the 

 N:mtili. luit dibranchiate decapods, h:iviiiLi tin ' allinity 



to the Spirnhe. As early as 1867, Barnmde had shown the small 



resemblance that exists between the Goniatites and tin- Nautilid;e. 



during the first period of their development. Tin- initial cham- 

 ber of (lie phragmostraonm in tin- Nautilida-. doe- IK. l sensibly 

 dilfer. iii its m-iicr;il <>ri:;iiiixnt inn. IVniii the ntln-r priiiirii-y rli.-nn- 

 bers Which are developed a little later; whereas the initi.-d >liell 



oi'the Gk>niatites appears in thr lonn nl'mi t j 'i<i. isolated iVnm UK- 



lirst iiir-clianiliei- ly:i dist inct, const net ion. This initial chanilter 

 nr <>vi->:ie. of the (inniatitcs, so diU'ei-ent (Voin those which imme- 

 diately sneeeod it. is met with at the origin of the |>hrai:-i!io>t r:i 

 ciiin of all the dilranchiato, niollnsca that M. M unier-( 'halnia- 

 ha- lieen ablr to study. Mi'. Alphens Hyatt's very intcrrsl inn 



invent i^ations upon the embryogenj of the phragmostraeum <>t' 



Xdit/t'ht* /'niHfu'litiK, /)<-r<n-r.rtix />ld ti/<-oxf<i, and tlie ( Joniat it -s. 

 come in support, of these observations. Mi 1 . Hyatt, however, 

 preoccupied by his theoretical ideas upon the evolution of living 

 ereaturcs. in order to establish the atliliation of the Ammonite 

 and Nautili, supposes that, the latter lost their ovisac by ti'imca- 

 tion. To support this supposition, he adduces the transverse 

 external cicatrix which he observed on the initial chamber of 

 .\V////////s J'lini/iiltiix. The comparative examination which M . 

 Munier-Chalmas has made oi'the ovisacs of >S'/>//-///^/ /><>,, /it and 

 of Ammonites Parkintsoni, a&d other species, has shown that in 

 these mollusks the siphon originates in the ovisac a little before 

 1 he appearance of the first, septum. It commences by a c;ec:d 

 inflation, which bears the prosiphon in its prolongation. The 

 new orpin, to which he o-jvrs the name of prosiphon. must take 

 the place of the siphon during the embryonic period. It 

 originates in the ovisac. opposite the siphonal inflation, upon 

 which it terminates, but without having any internal eoininuni- 

 eation therewith. It is very variable in its general form, and 

 may present st ron'ly marked examjiles of dimoi-phism in the 

 same ^pecies of Ammonite. It is formed ly a membrane, which 

 is -ometimes simply spread out as in ,S'//V///f/ l } >', <,,/</. or which 

 ma \' form a more or ICSN circular tube. It also presents two. 



