218 





The result of his analysis is 





in which 



aiid/'(<T) is a discontinuous function, which is supposed to 

 vanish when cr Z 1 . 



As particular examples of this result, the author deduces 

 the attraction of an ellipsoid on an external or internal point, 

 when the force varies as the inverse square and as the inverse 

 fourth power of the distance. In the latter case some re- 

 markable consequences are seen to flow from the discontinuous 

 character of the functiony(o-). When the density is uniform, 

 and the point external, all the elements of the integral which 

 precede or follow the break in that function vanish, while at 

 the break a single finite element occurs. This gives a finite 

 algebraic expression for this case of an ellipsoid's attraction. 

 When the ellipsoid is of variable density, and the point exter- 

 nal, the attraction is given partly by a finite algebraic expres- 

 sion, and partly by a definite single integral. 



Similar remarks apply to all inverse even powers of the 

 distance, except the square. 



Dr. Allman read a paper on the larva state of Plumatella, 

 and on the anatomy of Polycera quadrilineata. 



In this paper the author described the occurrence in Plu- 

 matella fniticosa, Allm., of a larva state presenting a very 

 difi'erent form from that assumed by the mature animal. This 

 larva was discovered in a glass of water containing specimens 



