310 Prof. Owen on the Structure of the Pearly Nautilus. 



and sessile. The circumference of the disc of the sucker is raised 

 by a tumid margin ; a series of slender folds of membrane, cover- 

 ing corresponding fasciculi of muscular fibres, converge fi'om the 

 circumference towards the centre of the sucker, where a circular 

 apertm'C leads to a cavity which widens as it descends, and con- 

 tains a soft caruncle, rising from the bottom of the cavity like 

 the piston of a syringe. AATien the sucker is applied to any sur- 

 face for the purpose of adhesion, the piston, which prenously 

 filled the cavity, is retracted and a vacuum produced. 



" In the Onychoteuthis the caruncle supports a long, curved, 

 sharp-pointed claw. These formidable weapons are sometimes 

 clustered at the expanded terminations of the tentacles, and in a 

 few species are arranged in a double alternate series along the 

 whole internal surface of the eight ordinary arms, as they were in 

 the extinct Belemnite. 



" In the diminished number, increased size and progressive 

 complication of the cephalic muscular appendages, and in their 

 final modification, in the two long superadded tentacula of the 

 Onychoteuthis, for combining with one another to produce a de- 

 terminate action, we trace the common order which regulates 

 the development of other parts of the animal organization. In 

 our past review of the Invertebrata, we have witnessed this law 

 in the appearance of the more essential organs, as the stomach, 

 the heart, the gills, the generative organs ; we find it equally re- 

 gulating the development of the peculiar prehensile instruments 

 of the Cephalopodic class. 



" At first very numerous, comparatively small and feeble, es- 

 sentially alike, the cephalic tentacles of the Nautilus strikingly 

 illustrate the principle of vegetative or irrelative repetition. Their 

 primary import is however plainly indicated by the du-ect deriva- 

 tion of their central nerve from the cephahc ganglion ; and they 

 present the same complex plan of arrangement of their muscular 

 fibres which characterizes the arms and tentacles of the Dibran- 

 chiate Cephalopods. The prehensile sm-face of the tentacula of 

 the Nautilus is made adhesive after the tj^e of the simple lami- 

 nated sucker of the Remora ; the median longitudinal impression 

 which partially divides the lamella may represent the complete 

 interspace which separates into two series, in the arms of most of 

 the Dibranchiates, the more complex suctorial appendages which 

 are developed on their internal surface : but at all events, the re- 

 duction of these arms in number, their augmentation in size, and 

 perfection as prehensile instruments by the superadded compli- 

 cations, are phfenomena which ordinarily attend the march of de- 

 velopment. The order of this progress would be anomalously 

 reversed if the tentacles of the Nautilus represented, as M. Valen- 

 ciennes supposes, the caruncles of the acetabula, and the hollow 



