28 VAN DER HOEVEN ON THE ANIMAL 
formed by two membranes, the external transparent, the inner thicker, coloured, brittle, 
and offering circular stripes or fibres. In the interior of the tube there was a thread or 
band, coiled up in a spire with close circumvolutions, like the spiral fibre of the trachee 
of insects. This fibre was not of exactly equal broadness in its whole extent; its broad- 
est parts had a diameter of nearly qth of a line. This fibre seemed composed of an 
external transparent membrane, including an internal part of a yellowish brown colour, 
Between the fibre and the tube containing it were observed several free microscopic 
parts ; some greater, of a brown colour, oblong or navicular ; some smaller, uncoloured, 
and still of different size. How different this conglobated tube, contained in the sper- 
matic vesicle, may be from the Needham-machines or spermatophores of other Cephalo- 
pods, I still believe that we ought to consider it as a similar sperm-containing apparatus. 
It is highly desirable that a travelling naturalist should have the opportunity of observing 
the male Nautilus in a recent state. 
Imperfect as they are, I trust those last observations to be still of some interest for 
comparative anatomy, as giving the first account of that which seems now to be the 
chief desideratum in our knowledge of the Nautilus, the disposition and structure of the 
male generative apparatus. 
DESCRIPTION OF THE PLATES. 
Figs. 1—8 belong to the female Nautilus ; figs. 9—14 to the male specimen, which is 
described at the end of my memoir. 
PLATE V. 
Fig. 1. A female Nautilus in its shell, from the left side. 
PLATE VI. 
Fig. 2. The same specimen seen from above, and taken out of the shell. 
Fig. 3. The same, from below. 
The following letters indicate the same parts in those three figures: a, the 
hood ; 6, the eye ; ec, the digitations ; d, the funnel ; FFf' i, the mantle ; 
i, its visceral part ; f’, the dorsal fold of the mantle ; g, the aponeurotic 
insertion of the shell-muscle. 
In figs. 1 and 3, h indicates the place where the laminated gland is situated. 
In fig. 2, h hh are three aponeurotic inscriptions on the visceral sac ; jis 
the siphon. 
PLATE VII. 
Fig. 4. Branchial cavity and funnel of the same. /f, funnel; g, mantle, reflected ; 
ee, shell-muscles ; A h, first pair; h! h', second pair of branchiz ; a, anus ; 
