240 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



time : one central synapse (0.006), plus muscle-plate arborization (0.003), 

 plus transmission time (0.003), plus delay in one cell body (.f) gives a 

 total time of 0.012 + x second. This is 0.016 + -"' second less than by 

 the path through the cord, or less than one-half. Any such estimate is 

 of course subject to a large error because of the inaccuracy of the data 

 on which it rests; however, the comparison suffices to show that the 

 Reissner's-fibre apparatus may be a great time-saver. It is evident that, 

 in the lower vertebrates particularly, this short circuit may mean the 

 saving of a considerable fraction of a second. 



In the struggle for existence an animal may be frequently presented 

 with ocular evidence of danger, the only safety from wliich lies in flight, 

 dodging, or some other quick reaction from the source of danger. A 

 decrease of a small fraction of a second in the reaction-time may often be 

 a matter of escape or injury, of life or death, and so the determining 

 factor in the survival of the fittest individual or species. The optic 

 reflex apparatus, then, not only plays an important part in the life of 

 the individual, but its functioning has probably often been a determining 

 factor in the evolution of vertebrates. 



The conclusions and the discussion of the results and bearings of this 

 research are reserved for the second part of this paper, dealing with the 

 higher vertebrates. This is already well advanced, and it is hoped will 

 appear in about a year. 



June, 1904. 



