PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONID.®. 39 
to the shells of this family. The outer coat of these valves is 
separated from the lower or normal portion by a small space 
filled by a cellular calcareous deposit, which is easily seen in 
a section of the valves/' 1 In 1869 Dr. W. Marshall 2 made a 
great advance in our knowledge. He found that the tegmentum 
of Chitons was perforated by a series of fine vertical canals, 
which open at the surface in a series of cup-shaped apertures, 
and that these vertical canals open into a series of horizontal 
canals running in the space between the apposed surfaces of 
the tegmentum and articulamentum, and that these canals 
opened on the under surface of each shell. He further found 
that the larger vertical canals, before reaching the surface, 
became enlarged and gave off each a crown of smaller canals 
also terminating at the surface in cup shaped apertures, and 
that the canals and apertures, small and large, are distributed 
evenly over the outer surface of the shell. He decalcified the 
shells, and found in the canal system ramifications of soft 
tissue, which he recognised as offsets of the mantle and con- 
sidered homologous with those of Balanidse and Brachiopods. 
He erroneously regarded the soft tissue ramifications as 
tubular and respiratory in function. In 188$ Van Bemmelen, 
following up his researches, examined the structure of the soft 
tissues contained in the shell of Chiton marginatus, and 
discovered that the tegmentum is entirely filled with papilli- 
form bodies which terminate the branches of the network and 
occupy the surface perforations described by Marshall. He 
figures and describes the structure of these papillae and their 
relations to the tegmentum, and propounds certain theories as to 
their homologies which will be referred to in the sequel. At 
the time at which I wrote my preliminary account of my dis- 
covery of eyes in the shells of the Chitonidae I was not aware 
of the existence of Dr. Marshall’s and Mr. Van Bemmelen’s 
memoirs, and thought that the papillae in the tegmentum were 
also new to science. I much regret that I should have inad- 
1 J. E. Gray, “ On the Structure of Chitons,” ‘ Phil. Trans.,’ 1848. 
2 W. Marshall, ‘‘Note sur l’histoire Naturelle des Chitons,” ‘Archives 
Neerlandaises des Sciences exactes et nat.,’ t. iv, 1869. 
