30 



March 5, 1851. 



Dr. D. H. Storer, Vice-President, in the Chair. 



Dr. Kneeland read a communication from Mr. Charles 

 Girard on the Organs of Vision and the Nervous System 

 in the embryo of Ascidia, as follows : — 



Every one conversant with the development of Ascidia will 

 recollect that dark, ovoid, or spherical body of early appearance 

 in the embryo, designated under the name of " Oculiform 

 spot:' 



" Within the thickness of the external layer," says Van Bene- 

 den, "appears about in the middle ofihe body and a little above 

 that region, a cell filled with black pigmentura, which cannot 

 but be considered as the organ of vision."* And a little further: 

 "It persists during the whole period of wandering life, to dis- 

 appear after the young has become fixed." 



Indeed, it seems at first quite natural that an animal which 

 moves freely about when young should have an eye, or an or- 

 gan of vision that is not wanted when it fixes itself for 

 the remainder of its life. But how far is this view consistent 

 with the fact that the oculiform spot reaches its maximum of 

 development before its escape either from the egg or the body 

 of the parent; and with that other fact, that eye specs exist in 

 the adult and immovable animal upon a region quite remote 

 from the original situation of the oculiform spot in the embryo. 



It is well known that in some species of Ascidia eye specs 

 are observed around the external openings of the cavity of the 

 body, four, six, or eight and more in number, and that these eye 

 specs do not exist during early life, but gradually appear and 

 develop as the animal approaches its full grown state, when it 

 attaches itself to some submarine body. 



The oculiform spot belongs to the internal layer of the em- 

 bryonic substance and not to the external one, as supposed by 



* Recherches sur rEinbryogenie, I'Anatomie, et la Physiologie des Ascidies Sim- 

 ples. Memoires de I'Academie Royale des Sciences, Belles-Lettres, and Beaux 

 Arts de Belgique. Bruxelles, 1S47. 4to. (fig.) 



