ANATOMY AND LIFE HISTORY OF MOLLUSCA. 127 



have been noticed in the veins of the Mollusca ; and in these small 

 capillaries, it is the only instance in which I have been able to 

 perceive them. The fact, in any case, has a most special interest 

 as occurring in the shell-structure, where I do not find that any 

 author has suggested the existence of blood circulation. The 

 tubes were ultimately merged in the thickened shell-structure. 



Multiplicity of Eyes in Mantle and Shell. — It is nearly 

 a century since Poli (" Testacea utrisque Sicilian," p. 153,) 

 noticed the occurrence of certain organs like the human eye in 

 the mantle of Pecten. This, after a long interval, was a subject 

 taken up by many observers, and extended to other genera, such 

 as Area, Prctunculus, and Cardium. In 1877 Dr. Karl Semper 

 published the important discovery that he had made, of eyes in 

 the dorsal papilla of certain species of Onchidium, while it began 

 to be realized that Mollusca generally were better provided with 

 visual organs than had ever been imagined; but the shell was not 

 thought to be the place where they would be found to reside. To 

 use the words of Prof. Mosely, "A Molluscan shell is, moreover, 

 almost the last place in which the naturalist would expect to find 

 eyes, and the Chitonidse have hitherto in text-books always had 

 the absence of eyes assigned to them as one of the characteristics 

 of their group." 



It would be unjust not to mention the labors of other observers 

 in the same field, and therefore the following extract from 

 Prof. Mosely (Quarterly Journ. Microscop. Science, 1885, p. 38,) 

 becomes necessary: — "Middendorf ('Beitrage zu einer Malaco- 

 zoologia Bossica.' ' Mem. de l'Acad. de St. Petersbourgh Sc. Nat.' 

 Ser. iv., t. vi., 1849.) named two distinct layers, of which the 

 shells of Chitonidse consist, the tegmentum and articulamentum ; 

 and Dr. W. B. Carpenter examined the shells of Chitons by 

 means of sections, and observed the perforate structure of the 

 tegmentum in Chiton, writing as follows : "In Chiton the external 

 layer, which seems to be of a delicate fibrous nature, but which is 

 of extreme density, is perforated by large canals which pass down 

 obliquely into its substance, without penetrating however as far 

 as the middle layer. (Dr. Carpenter has kindly lent me his 

 original sections of Chiton shells, and from what I now know 

 I am able to recognize parts of pigmental eye-capsules in one 

 labelled Chiton spiniqer)." (" Cyclopaedia of Anatomy and 

 Physiology, Article Shell," p. 565.) The late Dr. Gray wrote in 

 his paper on the "Structure of Chitons": — "The greater number 

 of species have a part of the valve which is not covered by the 

 mantle, but exposed. This exposed part consists of a perfectly 

 distinct external coat, peculiar I believe 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 



