1893. OWEN. 29 
period of growth antecedent to the acquisition of the procreative 
functions, or the adult stage of existence, and that these early 
chambers are relatively deeper than the succeeding ones. 
In this comprehensive review of the subject Professor Owen 
states that he ‘holds by the opinion expressed in his original memoir 
and in the ‘ Catalogue of the Fossil Cephalopoda in the Hunterian 
Museum’ (4th ed., 1856, p. 29), that they so affect the specific 
gravity of the active, highly-organised, cephalopodous mollusc, as to 
enable it with little éffort to rise, in the case of the Nautilus, from 
its habitual position at the bottom of the sea, and in the case of the 
Spivula, to sink from its more usual zone at or near the surface, 
by means of the hydrostatic mechanism worked by the muscular 
forces of the mantle and funnel. The constancy of the siphuncular 
connection running through all the chambers of the largest and 
most complex of the polythalamous shells, with the great size and 
singular complexity of the siphuncle in several extinct species, form 
the grounds on which I still hold to my original belief in the function 
of the siphuncle as related to a maintenance of the vitality of the 
shell.” 
In the following year, Professor Owen published the results of his 
dissections of a perfect specimen of Sfivula austvalis received from 
Mr.Cuming. The animal was described as almost as devoid of external 
organs of natation as Nautilus. In both, the direction in which such 
forces act is retrograde. Nautilus exercises them mainly by virtue of 
the muscular funnel, through which it forcibly ejects into the sur- 
rounding water the respiratory current. Sfzvula superadds to this the 
ejection of that volume of water upon which the cephalic arms and 
their basal webs contract after the fashion in which the other 
Dibranchiata, especially the Octopods, propel themselves backwards. 
Spivulais superior to Nautilus in the cephalic mechanism. In both 
instances of multilocular cephalopods, the natatory power is inferior 
to that of existing Dibranchiata. The distinction, therefore, between 
Nautilus and Spivula in regard to the shell in its protective relation is 
relative not absolute: in the one a small proportion of the shell is 
occasionally “internal,” in the other a small proportion is always 
“external,” in both the multilocular shells correspond with the 
phragmacone of the Belemnite. The tetrabranchiate Orthoceras may 
be called a representative analogue of the dibranchiate Belemnite, as 
the tetrabranchiate Ammonite is of the dibranchiate Spivula. The 
siphon is ‘‘ ventral’ and marginal in both kinds of coiled shells, but 
it runs along opposite sides of the coil. In Sfivula, its position is 
internal, or ento-marginal; in ammonites, it is external or ‘“ ecto- 
marginal.” 
In 1883 the veteran anatomist published a paper on the ‘‘ Aspect 
of the body in Vertebrates and Invertebrates,” which formed, we 
believe, his last contribution to the anatomy of the invertebrated 
animals. His researches cover a period of fifty years and afford 
