448 Benjamin Sharp 



Historical. 



In working iip the literature of this subject, I find, that with the 

 exception of Will and Siebold , ali the authors have confined their 

 attention to the asiphonated forms and especially to the well known eye 

 of Pecten. 



J. X. PoLii in 1795 was the first to mention the fact that any of 

 the Lamellibrcmchiata possessed eyes. He pointed out that Ostrea [pec- 

 teti) jacohaea and Spondijlus gaederopus possessed small bright ocelli 

 distributed on the edge of the mantle in considerable numbers. He 

 figures and gives a short account of their external anatomy. 



In 1834 R. Gakner2 describes the eyes oi Pecten, Spondylus, and 

 Ostrea as being »small, brilliant, emerald-like ocelli , which from their 

 structiire, having each a minute nerve, apupil, apigmentum, a striated 

 body and a lens : and from their Situation at the edge of the mantle, 

 where alone such organs could be useful, and also placed as in Gastro- 

 poda with tentacles, must be organs of vision«. As far as this goes it 

 is correct and is the first description of the minute anatomy of this 

 organ. 



In 1840 two authors added to our knowledge on this subject, 

 A. E. Grube 3 and A. Krohx. The former laid down the law that in- 

 vertebrate as well as vertebrate auimals that are free to move about in 

 the air or water , possess eyes in order to recognize their surroundings 

 and to direct their movements ^. 



He then says that snails possess eyesight and that acephales are 

 blind and this is owing to their stationary condition. The only two ge- 

 nera, among the acephales, according to Grube, that can see are Lima 

 and Pecten and these do not form exceptions to the rule as they have 

 the power to move about from place to place by clapping their shells. 

 He then enters into the anatomy of the eye and considers it in the three 

 forms of Pecten Jacohaeus, P. opercularis and P. varms. 



' J. X. Poli, Testacea utriusque Siciliae eoniinque hìstoria et anatome tabu- 

 lis aeneis illustrata. Parmae 1795. Voi. II. p. 107. Spotidt/lus Tabula XXII fig. 1, 

 2, 4 et 5. Pecten Tabula XXVII fig. 5, 14 et 1.5. 



•^ R. Garner , On the nervous system of molluscous animals. Trans, of the 

 Linnean Society. Voi. XVII. Pt. IV. p. 485 et seq. London 1834. p. 488. 



3 A. E. Grube , Über Augen bei Muscheln. Müller's Archiv für Anat. und 

 Physiol. Berlin 1840. p. 23 ff. 



* »Dass Thieren mit freierer Ortsveränderung in Luft oder Wasser Augen 

 gegeben sind, um ihre Umgebungen zu erkennen und danach ihre Bewegungen 

 einzurichten.« 



