II. 



Biological Theories. 



v.— SUGGESTIONS AS TO THE TRUE FUNCTIONS OF "TENTACU- 

 LOCYSTS," "OTOCYSTS," AND "AUDITORY SACS." 



SUCH a jelly-fish as Aurelia has eight minute finger-like bodies 

 lodged in little pouches in the edge of the umbrella or swimming- 

 bell. The tip of each is weighted by a calcareous deposit within it, 

 and the stalk is hollow, the cavity of the gastro-vascular system 

 extending into it. To the whole organ, that is, to the diminutive 

 tentacle and its pouch together, the name " tentaculocyst " is applied, 

 and the function performed by the eight such organs is a subject 

 which 1 propose to consider first. 



The large nerve-supply has led to the belief that the tentacu- 

 locyst is a sense-organ, and it is not infrequently described as a 

 combined visual and auditory organ. That it is not auditory, I have 

 already shown. That it is sensitive to light is a reasonable conclu- 

 sion from the presence of pigment, but that does not explain its 

 structure. A simple pigment spot without pouch or tentacle would 

 serve that purpose quite as well. There is, moreover, a wide 

 difference between an organ sensitive to light and a visual organ, 

 for " sensitive to light " does not necessarily mean giving rise to a 

 sensation when light falls upon it. It may be that light produces a 

 stimulus when it falls on a pigmented patch, but unless that stimulus 

 gives rise to a sensation of some kind or other, the organ should not 

 be called visual. A reflex muscular contraction may follow upon 

 the stimulation by means of light, but that by no means shows that 

 sensation has intervened. Little as we know of the psychology of 

 these lowly-organised animals, we are justified in doubting, if not in 

 denying, the possibility of consciousness and, therefore, of sensation. 

 It is nearly impossible to believe that consciousness, and judgment, 

 and intelligent action upon the basis of knowledge received by means 

 of sense-organs is possible in an animal with a nervous system so 

 lowly-organised as that of a jelly-fish, especially of a Scyphomedusa, 

 and an explanation of the function of these organs which is free 

 from any such assumptions as these would, therefore, seem to be 

 called for. 



If, however, these were auditory organs, as has been supposed by 



