40 



more fixed condition of the eye in them, if the range of vision had not been ex- 

 tended in the manner above mentioned, viz. by the enlarged pupil. The prin- 

 cipal tunic of the eye is a tough exterior membrane or sclerotic (r. pi. 7.), thickest 

 posteriorly or where it is continued from the pedicle, and becoming gradually 

 thinner to the margins of the pupil. 



The nervous fibres after leaving the optic gangUons enter the pedicles and 

 form a tough pulpj' mass (s. pi. 7.) at the floor of the eye, which extends as far 

 forwards as the semidiameter of the globe. This nervous tissue as well as the 

 whole interior of the cavity is covered by a black pigment, which is consequently, 

 here, as in the Cuttle-fish, interposed between the impinging rays of light and 

 the sentient membrane. 



The contents of the globe, of whatever nature they were, had escaped by the 

 pupil. If it had ever contained a crystalline lens, that body must have been 

 extremely small ; as othera^ise, from the well known effect of ardent spirits in 

 coagulating it, it would have been readily perceived. Wliat adds, however, to 

 the probabiUty of this eye being destitute of a crystalhne humour, is the total 

 absence of ciliarj- phc?e or any structure analogous to them. In some parts of 

 the cavity a membrane could be distinguished which had enveloped the fluid 

 contents of the eye ; but it had entirely disappeared at the pupil, which had in 

 consequence freely admitted the preserving Uquid into the ca\aty of the globe. 

 Rumphius states that the eye of the Pearly Nautilus is filled with a dark brown 

 sanguineous fluid. In the present specimen it unfortunately happened, that the 

 right eye haAdng been torn off" by the boat-hook in the capture of the animal, 

 prevented a further and more satisfactory examination of this organ. 



In the simplified structure which has just been described, it is possible that the 

 actions of some of the parts may have been so modified as to compensate more 

 or less for the absence of others which are usually deemed essential to complete 

 vision ; otherwise we must suppose the sense of sight in the Pearly Nautilus 

 to be reduced to the simple consciousness of the reception of light. But even 

 this act, unless the pigment be traversed by nervous fibrils too minute to be 

 detected, is performed in a manner incompatible with the ordinary idea of the 

 mode in which the retina is affected by luminous rays. I am not aware that 

 any satisfactory explanation has been given of this anomalous disposition of the 

 black pigment by those who have made the eye of the Cephalopoda a peculiar 



