48 MARINE BIOLOGICAL LABORATORY. 



until at last, stripped of one disguise after another, they 

 have been almost, if not quite, reduced to the level of 

 the sensory nerves of the trunk and hind head, through 

 the researches of Marshall, His, Beard, and others. 

 The identification of this pair of nerves with the rest 

 of the segmental sensory nerves, on the basis of de- 

 velopment and structural features, is a triumph of 

 investigation so near at hand that it is scarcely pre- 

 mature to proclaim it. The chain of discoveries bear- 

 ing on this subject has still many links to be supplied, 

 and here is one of the opportunities of the hour. 



The optic nerves still hold undisputed possession of 

 the very pinnacle of isolation ; and even to question 

 their claim to such a position may appear to betray 

 a woful superabundance of speculative audacity that 

 would be less unbecoming to a romancing visionary 

 than to the sober investigator. But without hesitation 

 or misgivings, and without any special claim to scien- 

 tific prevision, I venture to predict that these nerves 

 and their sense-organs will yet fall into line with the 

 other sense-nerves and sense-organs. 



I cannot here enter very far into the question of the 

 origin of the vertebrate eyes, but the subject is one 

 of such great interest, that, at the risk of overtaxing 

 your forbearance, I venture to ask your indulgence for 

 a few general remarks. The evidence in favor of the 

 derivation of the organs of the special senses from a 

 common basis, has been growing during the past few 

 years with such astonishing rapidity, that the hypothesis 

 of independent origin has no longer a respectable claim 

 to attention. If the eyes have been derived from some 

 simpler form of sense-organs possessed by the ancestors 



