Miscellaneous. 75 



outer capsule of the eye, and bears the cornea : another more closely 

 envelopes the retina ; it is cartilaginous, serves for the attachment of 

 the muscles of the eye, and reminds us of the sclerotic ring of birds 

 and reptiles. Even in the Nautili, however, there no longer remain 

 any of these homologous parts of the sclerotic. In the other Mol- 

 lusca it would be very difiiciilt to say what we are to regard as the 

 sclerotic. It is equally impossible to distinguish a cornea in them. 

 We cannot say, indeed, that the essential character of the cornea is 

 its being the first refractive medium in the eye. The serpents teach 

 us the opposite of this, since in them the first refractive medium is 

 formed by the eyelids. Moreover, in a great number of MoUusca, 

 the region which is usually designated by the name of the cornea 

 does not present any greater transparency than the rest of the en- 

 velopes of the eye. 



In the Vertebrata, on the contrary, the cornea has a very definite 

 meaning, especially as, from the observations of M. Hensen, it pre- 

 sents a development sui generis. In the embryo, immediately after 

 the invagination of the crystalline, this anatomist has seen the 

 cornea appear as a very delicate basilar membrane of the epithelium. 

 As long as the crystalline still contains a cavity there exists between 

 it and the cornea, in front of the pupillar membrane, a sort of gela- 

 tinous tissue, exactly similar to that of the vitreous body at the 

 same embryonic period. Neither the sclerotic nor the choroid has 

 any connexion with a similar tissue. 



It is equally difficult to determine the homologue of the choroid 

 in the Mollusca, In the Vertebrata this membrane is at once vas- 

 cular and pigmentary. The concordant investigations of MM. Kol- 

 liker, Hensen, Schultze, and Steinlin show clearly that the black 

 epithelium of the choroid is in reality a dependency of the retina ; 

 it is formed, in fact, by the outer lamella of the primitive ophthalmic 

 vesicle. M. Hensen asserts that he has ascertained that the cones 

 and bacilli are produced by this epithelium and not by the rest of 

 the retina. Hence the principal character of the choroid is vas- 

 cularity, and the name of vasculosa has frequently been given to it 

 in human anatomy. From this point of view it would be impossible 

 to find the least trace of a choroid in the Invertebrata. The intra- 

 retinic pigment layer of the Mollusca in particular by no means 

 merits the name of choroid. 



It is generally supposed that the ophthalmic vesicle which sub- 

 sequently forms the retina is nothing but an extravagination of 

 the central nervous system. The embryological researches of M. 

 Hensen tend not only to confirm this view, but also to establish a 

 complete parallel between the different layers of the retina and those 

 which primitively form the central nervous tube. — Archiv fiir 

 mikr. Anat. Bd. ii. 1866, p. 399 ; Abstract by E. Claparede in Bibl. 

 Univ. November 25, 1867, Bull. Sci. pp. 268-271. 



Adanson's Black Crocodile. By Dr. J. E. Grat. 

 Dr. Alexander Strauch asserts that Adanson's " Crocodile noire " 

 is not Crocodilus frontatus, but C. cataj^hr actus, Adanson mentiflfift 



