128 ANATOMY AND LIFE HISTORY OF MOLLUSCA. 



calcareous deposit, which is easily seen in a section of the valves. 

 (J. E. Gray "On the Structure of Chitons," Phil. Trans., 1848.) 

 In 1869, Dr. W. Marshall ("Note sur l'histoire Naturelle des 

 Chitons," " Archives Neerlandaises des Sciences exactes et nat." 

 t. iv., 1869,) 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 

 recognized as offsets of the mantle, and considered homologous 

 with those of Balanidse aad Brachiopods. He erroneously 

 regarded the soft tissue ramifications as tubular and respiratory 

 in function. In 1882 Van Bemmelen, following up his researches, 

 examined the structure of the soft tissues contained in the shell 

 of Chiton marginatum, and discovered that the tegmentum is 

 entirely filled with papilliform 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." 



The really important discovery as to the nature of these organs 

 was made by Prof. Mosely himself. In examining a specimen of 

 Chiton (Schizochiton) incisus, Sowerby, he was struck with the 

 resemblance of the minute dots already mentioned to eyes, and 

 further examination proved that such was really their nature. 



On searching for eyes on the shells of other Chitonidye, he 

 found them present in the majority of the genera, differing 

 however in each genus more or less in structure and arrangement. 

 Mr. Mosely announced his discovery in the " Annals and 

 Magazine of Natural History " for August, 1884 (Vol. xiv., 

 5th Series, p. 141). ' The following is an abbreviated account of 

 these wonderful organs : — 



They are circular or oval in outline, varying in measurement 

 from T \-§ to e u"o of an inch in diameter, according to the sub-genus 

 or species. They appear under reflected light as convex, circular, 

 raised dots of highly refracting transparent matter, surrounded 

 by a narrow zone of pigment, or the margin of the choroid seen 



