STABILITY OF THE UKNERA. .')0 



cicatrice is the vestiiic of an openinjj,- wliich i)lace(| tliis ovisack 

 in communication witlitlie initial air-cliauilicr of llic shell ; lnil, 

 lie has never seen this siii)})ose(l ovisaek, whicli is h_v])othetical. 

 For him. tlie Nautihis is a ceplialoijod wliicli has lost its ovi- 

 saek. 



In Ammonites and (ioniatites t he initial disposition is entirely 

 different. The ovisaek is jjlainly visihle. olohular or ellipsoidal, 

 more dilated than the part eonli-^nous to the chambered spire. 

 No appearance of a cieatriet". It sutliees, consequently, to 

 examine the first chamber of a ei'plialoi)od to class it aniong the 

 Nautilides or the Ammonides and Goniatides. 



M. Barrande has shown that the initial appeaiance of the shell 

 of Nautilus is exhiliited without any change throngh all the 

 geological periods to the ])resent time. The fissure is supposed 

 by M. Barrande to lia\i' placed the mollusk contained in the 

 initial chamber in coniniunieaiion with a transitory organ, either 

 a vitelline vesicle (which, to M. Fischer, apjjcars inadmissible) 

 or to a natatory l)ladder. etc. 



P'rom the first appearance to ihe linal extinction of the (Jonia- 

 ti(he and Ammonitid?e. they always show a typical ovisaek ; it is 

 Iherefoi-e impossible to deri\'e them from the Nautilid;e. as sup- 

 posed l)y the developmentalists. This difference has induceil M. 

 Munier-Chalmas (Comptes Bendiis. Dec. 2t)th. iSTo) to separate 

 the two former from the tctrabranchiate or tentaculiferous eephal- 

 o|)oda (Nautilidie). and to nniie them with the dibranehiale or 

 acetal)uliferous grou)) (Spiiuli(he and Belemnitida-). which are 

 j)rovided with an ovisaek. 



Tt still remains to ascertain whethei' the presence or absence 

 of IIk' ovisaek has the systematic importance attributed to it ; 

 what is its nature and what is the purpose of the cicatrice. The 

 word ovisaek may be badly chosen because it supposes the 

 existence of calcareous enveloi)es to the eggs. 



One might discuss and wonder a long time on this subject 

 until a direct observation on the embryogeny-of Nautilus shall 

 give us the true solution. It is thus that the question of the 

 parasitism of the Poulpe of the Argonaut was agitated with 

 ardor until the day that Duvernoy showed the embryo of 

 Argonaut to be provided with a shell in the i^gg. 



