PRESENCB OE EYES IN SHELLS OP CEETAIN CHITONIDiE. 5 
to thè shells of this family. The outer coat of these valves is 
separateci from thè lower or normal portion by a small space 
filled by a cellular calcareous deposit, whicli is easily seen ia 
a section of thè valves/^ ^ In 1869 Dr. W. Marshall ^ made a 
great advance in our knowledge. He found that thè tegmeutum 
of Chitons was perforated by a series of fine vertical canals, 
which open at thè surface in a series of cup-shaped apertures, 
and that these vertical canals open into a series of horizontal 
canals running in thè space between thè apposed surfaces of 
thè tegmentum and articulamentum, and that these canals 
opened on thè under surface of each shell. He further found 
that thè larger vertical canals, before reaching thè surface, 
became enlarged and gave off each a crown of smaller canals 
also terminating at thè surface in cup shaped apertures, and 
that thè canals and apertures, small and large, are distributed 
evenly over thè outer surface of thè shell. He decalcified thè 
shells, and found in thè canal System ramifications of soft 
tissue, which he recognised as olfsets of thè mantle and con- 
sidered homologous with those of Balanidse and Brachiopods. 
He erroneously regarded thè soft tissue ramifications as 
tubular and respiratory in function. In 1882 Van Bemmelen, 
following up bis researches, examined thè structure of thè soft 
tissues contained in thè shell of Chiton marginatus, and 
discovered that thè tegmentum is entirely filled with papilli- 
form bodies which terminate thè branches of thè network and 
occupy thè surface perforations described by Marshall, He 
figures and describes thè structure of these papillse and their 
relations to thè tegmentum, and propounds certain theories as to 
their homologies which will be referred to in thè sequel. At 
thè time at which I wrote my preliminary account of my dis- 
covery of eyes in thè shells of thè Chitonidse I was not aware 
of thè existence of Dr. Marshall’s and Mr. Van Bemmelen’s 
memoirs, and thought that thè papillse in thè tegmeutum were 
also new to science. I much regret that I should bave inad- 
* J. E. Graj, “ On thè Structure of Chitons,” ‘ Phil. Trans.,’ 1818. 
“ W. Marshall, “Note sur l’histoire Naturelle des Chitons,” ‘Archives 
Neerlandaises des Sciences exactes et nat.,’ t. iv, 1869. 
