218 
»_2 pie 2 
ay ts on _ | 
—— =. 1. 
n 
he he. +h 
The result of his analysis is 
Reo d aie 
fig yPaasten ds (=) J(e) 
—\— r 5 = a Ley tao ee ss ‘ 
(2) at Tihs § (s+h,?) (s+h2’) ..(s+h,?) } 29 
in which 
IE eg fig x, ae 
oa het eet eb 
and f(o) is a discontinuous function, which is supposed to 
vanish when o 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 function f(¢). 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 fruticosa, Allm., of a larva state presenting a very 
different form from that assumed by the mature animal. This 
larva was discovered in a glass of water containing specimens 
