NOMENCLATURE OF STAGES OF GEOWTH AND DECLINE. 9 



exact relations with the indubitable protoconchs occurring upon the apices of the 

 conchs of Ammonoids and Belemnoids. The wrinkled lump above referred to is 

 unquestionably a part of the shell. It is not only closely attached, but the longi- 

 tudinal stride of the apex of the true conch are continuous upon the proximate 

 parts of the lump. It had an aperture which must have remained open until the 

 body of the veliger had entirely left the interior of the protoconch, and was 

 then closed by the apical plate. There is a cicatrix upon the apex of the conch, 

 which is invariably concealed by the lump when it is present, and in some 

 examples we observed the fracture of the outer layer of the shell on the apex 

 of the conch and outside of the ordinary boundary of the cicatrix, which could 

 only have been caused by the violent removal of the lump. The wrinkled and 

 contracted aspect of the lump when preserved can be accounted for by assuming 

 it to have been composed of conchiolin. This also accounts for its almost invari- 

 able absence, since such an organ must have been easily lost or destroyed. The 

 lumps must consequently be regarded as the remnants of conchiolinous pro- 

 toconchs having elongated and narrow apertures; but probably they were, 

 when in a living condition, much larger and more oval, and more similar to the 

 protoconch of the Ammonoids. The continuity of the striae from the conch to 

 the protoconch also shows that the conch was built out from the aperture of the 

 protoconch, layer after layer, and the concentric markings, and form of the apex, 

 which correlates with that of the scar, sustain this idea. The figures on the fol- 

 lowing pages are less perfect than several other examples studied by the author 

 since these were drawn. They do not show the passage of the external longitu- 

 dinal stria? from the apex of the conch on to the surface of the protoconch. 



A living chamber among recent and fossil Nautiloids marked a period of 

 rest after a stage of growth. The septum, therefore, was not built until the 

 animal arrived near the final steps, or had altogether stopped building out the 

 sides of that part of the shell in which it lived. At any rate, we can say with- 

 out risk of error that the septum was the final step, or one of the final steps, in 

 the construction of a living chamber. 



6. The first living chamber, or the first larval or naepionic 1 stage of a Nauti- 

 loid was, therefore, represented by the apex of the conch in that order ; but the 

 first septum and siphonal caecum did not exist at this stage, which is represented 

 by a straight or slightly curved widely spreading cone, — in fact, the empty apex 

 of the conch. The length of the first living chamber has not been ascertained ; but 

 that it was short seems probable from the form of the cone in Nautilus. Doubt- 

 less this remark does not apply to the earliest forms of closely coiled shells, in 

 which the cone was much slenderer than in existing Nautilus, and the first living 



1 NijTi-iof, infant, or young animal. The term " silphologic " was used for this stage in the article above 

 quoted. This literally means " grub " stage, and it is not strictly applicable to a normal progressive stage 

 of development. Grubs, caterpillars, and the like, among insects, are degraded or retrogressive develop- 

 ments, as compared with the normal, probably hereditary Thysanuriform larva; of what are commonly 

 called the lower orders of Insecta. Studies of insects lately made have convinced us of the truth of this 

 opinion, first published by Friedrich Brauer, and of the need of changing this term to the one used, and of 

 reserving silphologic as a general term for retrogressive stages, such as one finds in the larva? of Coleoptera, 

 Lepidotera, Hymenoptera, and Neuroptera. 



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