22 PROCEEDINGS OF THE AMERICAN ACADEMY 



yet succeeded in determifiing whether they were the identical 

 ones which were to be transformed into cartilage-cells, or 

 whether, on the other hand, they were the mother cells, from 

 which the cartilaginous cells would derive their origin. 



Mr. Agassiz further stated that he had examined the car- 

 tilage-like bones of fishes, of which Dr. Burnett had spoken, 

 and that he had found the same results. 



Professor Eustis gave an account of a formula for the 

 measure of the solidity of a prismoid, and its application to 

 other cases of mensuration. 



The ordinary formula for the area of a prismoid is J- h 

 {B -\- h -\- ^ TV/), where B and b represent the areas of the 

 upper and lower bases respectively, M the middle section, and 

 h the height. The application of this formula for the men- 

 suration of the sphere and the cone is alluded to in a recent 

 number of the Journal of the Franklin Institute. But still 

 more remarkable cases are those of the paraboloid, hyperboloid, 

 and ellipsoid of revolution, in which the prismoidal formula will 

 be found to give precisely the same results as those obtained 

 by the application of the ordinary formulas from the calculus. 

 Professor Lovering exhibited a new stereoscope just received, 

 and called the attention of the Academy to some points of 

 detail, especially those arising from the difference of effect 

 when the same drawings of a solid are viewed so as to repre- 

 sent it with one side or its opposite nearest to the eye. 



Dr. Burnett commented on these facts, as demonstrating 

 the proposition that the seat of vision is in the brain, and 

 not in the retina. 



Dr. B. A. Gould addressed some inquiries to Dr. Burnett 

 concerning the best spider-lines for use in the micrometers 

 of telescopes and microscopes. 



A discussion ensued upon the qualities necessary in spider- 

 lines for this purpose, in which Messrs. Bnrnett, Eustis, and 

 Gould took part. 



Dr. Burnett thought that the thread of the Attus or hunting 

 spider was the most desirable in all respects, having almost 



