100 STUDIES IN LIFE AND SENSE. 



These cells in turn represent the similar structures which occur in 

 higher animals, and which in man himself form the characteristic 

 terminations to his olfactory nerves. That the cuttlefishes can literally 

 scent their prey from afar off, is an idea confirmed by the facts of 

 their every-day life. A well-developed organ of smell necessarily 

 confers upon them a great advantage in the struggle for food in which, 

 along with the other tribes of the sea, they unquestionably share. 



The " ears " of the cuttlefishes present us with two sacs named 

 "auditory sacs" which may, as in the nautilus, either be attached 

 to the chief nerve-mass itself, or, as- in the two-gilled cuttles, be lodged 

 in special cavities in the gristly "skull." A cuttlefish "ear" is essen- 

 tially a sac or bag, called an "otocyst," containing either one or many 

 " otoliths n or " ear-stones," suspended in a watery fluid. This, 

 indeed, is the primitive type of "ear" we may find even in the 

 Medusidce or "jelly-fishes" themselves. The manner in which this 

 hearing sac exercises its functions is not difficult to trace. Vibrations 

 of sonorous kind, transmitted to its substance, set the otoliths in 

 motion. This motion, along with that of the contained fluid of the 

 otocyst, is communicated to the " end cells " bearing delicate pro- 

 cesses known as " auditory hairs " in which the fibres of the auditory 

 nerves end. Thus the " ear-sac " of a cuttlefish is simply a body 

 adapted for the reception of sound-waves, and for the modification 

 of these waves, which, as they impinge upon the fine ends of the 

 nerve-fibres of the sac, become transformed into impressions of sound. 

 These impressions are in due course transmitted to the brain; or 

 ganglionic mass of the animal, which, like that of other organisms, 

 acts upon the " information received " with an intelligence and com- 

 pleteness proportionate to the perfection of its structure and functions. 

 The ear-sacs of many cuttlefishes open on the external surface of the 

 body by two fine canals, named " Kolliker's ducts," after their dis- 

 tinguished discoverer. Occasionally these ducts end blindly, and do 

 not open on the body surface. These facts lend additional support 

 to the opinion that in the ear of the cuttlefish we find primitive 

 structures proper to the ears of vertebrates, the minute canals of 

 Kolliker corresponding with the recessus vtstibuli of the vertebrate 

 organ of hearing. Once again, therefore, we find the progressive 

 development of cephalopods and vertebrates running in parallel, but 

 nevertheless in distinct and independent, lines ; and this likeness is 

 further strengthened when we discover that not merely the ear, but 

 the eye likewise, of these two groups of animals is formed or developed 

 in an essentially similar fashion. The ear of the cuttlefish presents 

 us with a permanent example of an early and transitory stage in the 

 development of the vertebrate ear, and a common plan of ear-produc- 

 tion is thus seen to traverse a wide extent of the animal world. 



Those who are acquainted with even the superficial details of the 



