THE CEPHALOPODA. 
185 
Dr. Waagerij-^ in view of clearing away the difficulties that surrounded the question, 
dissected a female Nautilus pojitpilius, and has given beautiful drawings of the 
nidamental gland in that Mollusc, showing the abdominal surface of the Nautilus, 
the position of these glands, and their relation to the other viscera. After a carefid 
and exhaustive examination of all the anatomical facts disclosed by his dissection, he 
concluded that the Ajjfi/chus appears to have belonged to the nidamentary gland of the 
female Ammonite. 
In his recent memoir on the chambered shells of Cephalopods, Professor Owen^ 
reviewed in detail the various opinions expressed on the functions of the Aptychus, and 
remarked " in respect to the nidamental glands, that they are subject to seasonal changes 
and gain the relative bulk witii which the size of the aptychal plates accord only at the 
period of discharge of the impregnated ova, for which they have to furnish the protective 
coat or nidus. Such seasonal change is exemplified in the figure of these glands given 
in the 'Memoir on the Naatilus,' of 1832, and in that which is shown in taf. xix of 
Waagen's treatise in 1871. Moreover, in not one of the existing genera or species of 
Cephalopoda, Nautilus included, in which these glands are superadded to the more 
essential organs of generation, are they encumbered in any way or degree with such 
calcareous plates, as Keferstein's hypothesis applies to them in the Ammonite. 
" In the application of the anatomy of the constructor of the Pearly Nautilus to the 
solution of the problem of the nature and function of the Trigonellites I was led to regard 
them as the homologue of the organ, or a portion of the organ in Nautilus, which is of 
a fibrous texture resembling dense corium, called, from its shape and position, the hood 
(fig. 24), and which, when the animal had withdrawn into its dwelling, Avould serve as a 
rigid defence at the outlet of the shell. ^ It needed only that this part should be more 
or less calcified to form the preserved portions of an operculum like that ascribed to the 
Ammonite. The relative size of the Aptychis agrees with that of the shell. It has been 
found to measure seven inches six lines in length, and six inches in breadth, in gigantic 
Ammonites." [I myself have a specimen collected from the Middle Zone of the Lower 
Oolite which measures five inches in length and four in breadth, and probably belonged 
to a large Harjjoceras Soiverbyi, which is the only Ammonite with a whorl of that size 
and shape found in the bed from whence it was collected.] 
" It may be doubted whether the nidamental glands ever increased in the same 
ratio ; and it is still less likely that they needed such defensive plates in their season of 
rest and attenuation. If, therefore, my homology of the symmetrical halves of the 
Nautilus hood with the parial Trigonellites {Aptychus, v. M.) be preferably accepted the 
supposition that these parts are calcifications of an Ammonite^s hood may be deemed 
1 " Ueber die Ansatzstelle der Haftmuskeln beim Nautilus and dem Ammoniden," ' Palseontographica,' 
Band xvii, p. 185, pi. xxxix, Cassel, 18f)7 — 1870. 
2 "On the Relative Positions to their Constructors of the Chambered Shells of Cephalopods," 'Pro. 
of the Zool. Soc. of London,' p. 955, 18/8. 
3 'Memoir on the Pearly Nautilus,' p. 12, pi. iii, fig. 1, 1832. 
