SPIRULA PERONII. 29 



Let us now turn from the section to the first chamber. This, as 

 I have said, consists of a small rounded body bounded on one side by 

 the first septum, through which bulges the end of the siphuncle or 

 fleshy tube, contained within the septal funnels. Munier-Chalmas (12) 

 has described a little membraneous tube which stretches through the 

 empty chamber and forms a prolongation of the siphuncle, which he 

 calls the r p t rosi r plion. I have soaked the first chambers of several 

 specimens in refractive media, so that they became transparent, 

 and have also broken open some with needles, but I have failed 

 to see this prosiphon which thus apparently can only be seen in 

 exceptionally preserved specimens. It is also said to occur in the 

 first chambers of the Ammonites. 



I have purposely not called the first chamber the protoconch, by 

 which it is usually known, because there are three distinct things 

 united under the name. First, there are the primary chambers of 

 the Ammonites, to which I propose to limit the name protoconch. 

 These are little miniatures of the adult, ivithin which the first 

 septum is formed ; the walls are continuous with those of the succeed- 

 ing chambers^. 



Secondly, there are the forms exemplified by the first chambers 

 of Sjyirula, Belemnites, Goniatites (Mimoceras) compressus, and the 

 lately described form of Othoceras^, for these I propose to revive the 

 term " ovicell," because they stand in the same relation to the adult 

 as the egg-shell does to the bird. In these the form is inflated and 

 sharply constricted off from the succeeding chamber, with whose 

 walls it is not continuous ; the first septum is found at the apex, and 

 not within the chamber. The embryo, in emerging, apparently 

 gnawed a hole in the egg out of which it squeezed, and reared the 

 adult shell with this as its basis. As the above mentioned Othoceras 

 teaches us, the Nautili had eggs of this sort, but they usually 

 discarded them ; in some it seems to have been retained for a con- 

 siderable time, and the place of attachment is marked by a scar, as 

 in the recent Nautilus ; but in others, often closely related to forms 

 with the cicatrix, the apex is smooth^, showing that in these the 

 animal must have lived some time in a naked state, as the more 

 highly organized Ammonites certainly did. 



Thirdly, there is the type exhibited in Nanno (Endoceras) 

 belernnitiforme, Hohn( 16 ), which is of such a size that in cross section 

 it is more than half the size of the adult. Now we know that among 



(12). Comptes Bendus, vol. Ixxvii, 1873, p. 1557. 

 (13). Brown, Proc. Acad. Nat. ScL, Philadelphia, 1892, p. 139. 

 (14). Clarke, American Geol., vol. xii, 1893, p. 112. 



(15). De Koninck, Calcaire Carbonifere, Ann. du Mus. roy. de Belcjique, 1850. 

 (16). Hohn, Dames and Kayser's Pal. Abhandl, vol. iii, 1885 ; Clarke, Amer, 

 Geologist, vol. xiv, 1894, p. 205 ; Bather, Nat. Sci., 1894, p. 422. 



