694 William Patten 



tive part, so miicli larger than is necessary ; it should only be as large 

 as the axial nerve , and surely not largar in one place than another. 

 Then again the axial nerve, in other animals without doubt, 

 is not the sensitive element, but only the radiating and in- 

 finit ely smaller fibrilla e. In Cephalopods , the axial nerve is 

 entirely protected from the light by a eoating of pigment granules. 

 Moreover in ali other animals , the rays of light act at right angles 

 lipon the fibrillae, and there is no reason to suj^pose that in Arthropods 

 a different eondition prevails ; in faet we meet with insurmountable, 

 physiologìeal difficulties, in attempting to imagine the effect a ray of 

 light will produce, aeting parallel with a long and large nerve fibre. 



Indeed the objections to Müller's theory, as advocated by Exner, 

 Grenacher and Carrière, and almost universally accepted by modem 

 Zoologista, might, in the light of the facts given above, be multiplied 

 indefinitely without Coming to any more decisive conclusion. It will be 

 sufficient , I believe , for the present , to allow the matter to rest until 

 the observations , upon which my views are based , shall bave been 

 confirmed, or proved to be incorrect. 



I must again warn against the Interpretation given to results ob- 

 tained by superficial, physiological experiments upon the Arthropod eye. 

 Such results should be accepted with the greatest caution. The effect 

 produeed by any change in the amount of light. or by any 

 object, depends upon the structural perfection of the 

 visu al or ga n, and upon the associ ationof light im p res si ous 

 with the impressions received by other organs. To deter- 

 mine the functional perfection of a visual organ, we must know the 

 entire life history of the animai. How far we are as yet from such a 

 eondition is only too evident. Let a person offer a dog a stone, and it 

 would be a mere chance if the dog took any notice of it; this evidence 

 alone would be sufficient to prove, to some people, that the dog was 

 blind. Let our imaginary experimentor present him, after being fed, 

 with a piece of meat, and if no notice were taken of it, he would be 

 eertain that the dog was blind. If, on the contrary, the dog had, by 

 chance, been very hungry, the results would bave been different, 

 and any person would then come to the conclusion that the dog 

 could not only see well, but could actually distinguish between 

 things that were fit, or unfit to eat. This simple and perhaps unneces- 

 sary Illustration will, I think, enforce the statement already made that, 

 in such comparatively simple creatures as Insects and Arthropods, 

 whose actions are almost entirely controlied by so-called instincts, it is 



