On the Visual Organs in Lamellibranchiata. 449 



A. Krohn's ^ account is much fuller as to anatomy of the eye of 

 Pecten and goes far abead ofthat of any of bis predecessors. He was 

 the first to point out the existence of two nerves passing to the eyeball, 

 these two being the Splitting of the main nerve in the pedicle of the eye. 



In 1844 Will 2 investigated a number of Lamellibrancliiata and 

 found that a great many of them possessed eyes of great complexity. 

 I bave , unfortunately , been unable to consult the original article and 

 know it only through Troschel's Jahresbericht for 1844 3, and wbat 

 subsequent authors bave quoted or made reference to. 



C. Th. V. Siebold in bis Comparative Anatomy of the Inverte- 

 brata'^ sustains the observations of Will. 



It is bere said that the eyes of Pholas^ Solen, Venus and Mactra 

 are not on pedicles, but situated at the bases of the tentacles. In Car- 

 dium there is an extremely large number of contractile pedicles on the 

 ends of which are the eyes ; Tellina has the edges of the mantle set 

 with small pedunculated eyes of a reddish yellow color ; Pinna has on 

 the anterior mantle edge forty short pedunculated yellowish brown 

 eyes , while in Area and Pectimculus are a large number of brownish 

 red ones ; Anomia, a form not investigated by Will, has twenty brown 

 sessile eyes situated between the numerous tentacles ; in Ostrea the 

 visual Organs are the most numerous , and the most distinct eyes are 

 found in Pecten. 



M. DuvERNOY^ in 1852 gave a short description of the eye [of 

 Pecten maximus , but advanced nothing new on this head and did not 

 enter into the histology at all. 



1 A. Krohn , Über augenähnliche Organe bei Pecten und Spondylus. Mül- 

 ler's Archiv für Auat. und Physiol. Berlin 1840. p. 371 flf. 



2 Will, Über die Augen der Bivalven und Ascidien. Frgriep's Neue Noti- 

 zen a. d. Gebiete der Natur- und Heilkunde. Bd. XXIX. Weimar 1844. p. 81 

 und p. 99. 



3 Archiv für Naturgeschichte. XI. Jahrg. Bd. IL Berlin 1845. p. 297 : »Will 

 stellte Untersuchungen über die Augen der Muscheln an. Er fand dieselben sehr 

 hoch organisirt. Außer bei Pecien , Spondylus , Ostrea fand sie derselbe auch bei 

 Pinna, Area, Pectunculus , Mytilus, Cardium, Teilina, 3factra, Venus, Soleti. Pho- 

 las , zuweilen in ungeheurer Zahl. Auch bei den Ascidien Cynthia, Phallusia und 

 Clavellina wurden Augen nachgewiesen, und zwar 14, von denen 8 der Athem- 

 und 6 der Afterröhre angehören.« 



* C. Th. v. Siebold , Lehrbuch der vergleichenden Anatomie der wirbel- 

 losen Thiere. Berlin 1848. p. 262 u, 263. 



5 M. DuvERNOY, Memoire sur le Systeme Nerveux des Mollusques Acépha- 

 les, Lamellibranches ou Bivalves. Mém. de TAcad. des Sc. de linst, de France. 

 Tome XXIV. 1854. p. 69 ff. 



Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. V. 30 



