TO SANTA ROSIA AND SANTA MARIA 119 



These lively bivalves, like Lima and some allied 

 genera, possess a row of eyes upon their mantle 

 edges which, although not likely capable of clear 

 focused vision, nevertheless are extremely sensi- 

 tive to light stimuli. A passing shadow causes 

 every scallop instantly to close his shell, and any 

 attempt to seize one sets him darting about with 

 surprising quickness. Rapidity of movement and 

 ability to elude enemies is not in itself remarkable 

 even in quite low orders of life, but it is so in 

 Pecten, because they belong to a group of animals 

 (Pelecyopda) comprising many genera and thou- 

 sands of species of slow-moving creatures rarely 

 possessing traces of specialized visual organs. 

 If this apparent freakishness of nature were 

 carried out to the same degree among the higher 

 orders of animals, we would be justified in expect- 

 ing species of mammals with undeveloped sense 

 organs, or races of men with one eye centrally 

 placed, or possibly a row of eyes up and down the 

 spinal column or on the ends of the fingers. In 

 the lower orders specialized organs seem to be 

 easily attained or lost according to their use or 

 necessity in the vital economy of the species. One 

 is forced to the conclusion that all specialized 



