NATURAL SCIENCES OF PniLADELPHIA. 17 



February 3tZ. 

 Vice-President Bridges in the Chair. 



A letter was read from Rev. E. J. Lowe, dated Observatory, Beeston, 

 near Nottingham, (England,) Jan. 7th, 1857, containing the following 

 passage : — 



"The late Mr. Lawson, F. R. S., left rae his valuable collection of Meteoro- 

 logical Instruments, amongst which are Dr. Benjamin Franklin's Hygrometer, 

 which is in as good working order as on the day it was made, an Electric Kite 

 belonging to Dr. Franklin, and several letters. Mr. Lawson had a card placed 

 on the hygrometer, with the following inscription, ' Invented by and belonged 

 to Dr. Benjamin Franklin, the Patriot of Philadelphia.' I have mentioned this, 

 thinking that you would feel an interest as American Philosophers in the 

 information respecting the instruments of that glorious philosopher Dr. Frank- 

 lin." 



Communications were presented for publication in the Proceedings 

 entitled : — 



1. Descriptions of American land shells. By W. G. Binney. 



2. Prodromus descriptionis Animalium evertebratorum, qu?e in es- 

 peditione ad Oceanum Pacificum Septentrionalera a Republica Federata 

 missa, Joh. Rodgcrs duce, observ. et descripit W. Stimpson. 



3. On the Crania of the Ancient Britons, with remarks on the people 

 themselves. By Joseph Barnard Davis. 



Which were severally referred to Committees. 



Mr. Lea made the following remarks on the visual organs of certain 

 species of the genus Unio : 



He 'stated that he had at various times paid a good deal of attention to 

 the habits and organs of the Naiades of our own country, and for that purpose 

 frequently had them for long periods in a living state under his observation. 

 Their condition as to special sense has been of great interest, and particularly 

 those of touch, hearing and sight. In the course of these investigations, it be- 

 came evident to him that some species of Unio were sensitive to light, and he 

 found one species ( Unio radiatus) very eminently so. He stated that he was not 

 aware of its ever having been suggested that any of the family were possessed 

 of organs of sight, even in a young state, as in the case of the young of Mytilus 

 edulis. It is well known that some of the Molluscs have large and perfect eyes, 

 while some others have imperfect ones, but generally they are altogether devoid 

 of the optic nerve. The Sirombidce are said to possess an eye highly organised, 

 but in most of the Gasteropoda it is of a more simple structure, and perhaps only 

 possesses sensibility of light without the power of distinct vision. The terres- 

 trial Gasteropoda have usually a distinct eyeball on the extremity of the superior 

 tentacula, which Dr. Leidy has shown, in some of our species of Helices, to 

 possess a crystalline lens and choroidea, with clear, consistent, vitreous humor. 

 Cuvier and Lamarck considered the whole class of Conchifera to be devoid of 

 eyes, but Poll has shown that in Fecten varius, Lin., the margin of the mantle is 

 furnished with numerous eyes. These, according to Carpenter, are protected 

 by a sclerotic coat with a transparent cornea in front, a layer of pigment, a 

 crystalline lens and vitreous body, and a retinal expansion proceeding from an 

 optic nerve. In the course of his observations, Mr. Lea became satisfied that 

 the closing of the siphonal tubes, on his approach to the specimens he had in 

 his vivarium, was not altogether occasioned by the vibration caused by his ap- 

 proach, and he accordingly arranged numerous individuals of several species 

 with a view carefully to observe them. In the course of these e.xaminations 

 repeatedly made, he found several species of Unio quite sensitive to his passing 

 his hand between them and the light, while the Margaritana margarttifera, and 



1857.] 2 



