800 



to be enabled to place before our eyes, so to speak, the actual mo- 

 tion of the revolving body, yet it is not on such grounds that the 

 paper is presented to this Society. It is as a method of investiga- 

 tion that it must rest its claims to the notice of mathematicians ; as 

 a means of giving simple and elegant interpretations of those definite 

 integrals on the evaluation of which the dynamic state of a body at 

 any epoch can alone be ascertained. 



In these applications of the theory of elliptic functions, the au- 

 thor has been led to the remarkable theorem, that the length of the 

 spiral, between two of its successive apsides, described in absolute 

 space on the surface of a fixed concentric sphere, by the instantane- 

 ous axis of rotation, is equal to a quadrant of the spherical ellipse 

 described on an equal sphere moving with the body, by the same 

 instantaneous axis of rotation. 



The last section of the paper is devoted to the discussion of that 

 particular case in which the axis of the invariable plane is equal to 

 the mean semiaxis of the ellipsoid of moments. 



February 15, 1849. 



W. R. GROVE, Esq., Vice-President, in the Chair. 



A paper was in part read, entitled " Description of an Infusory 

 Animalcule allied to the genus Notommata of Ehrenberg, hitherto 

 undescribed." By John Dalrymple, Esq., F.R.C.S. Communicated 

 by Thomas Bell, Esq., Sec. R.S. 



February 22, 1849. 

 GEORGE RENNIE, Esq., Treasurer, Vice-President, in the Chair. 



The Right Honourable Sir Francis Baring, Bart., First Lord of 

 the Admiralty, was balloted for and duly elected into the Society. 



The reading of a paper, entitled " Description of an Infusory 

 Animalcule allied to the genus Notommata of Ehrenberg, hitherto 

 undescribed." By John Dalrymple, Esq., F.R.C.S. Communicated 

 by Thomas Bell, Esq., Sec. R.S. , was resumed and concluded. 



The examination of various specimens of the animalcule described 

 by the author, disclosed the dioecious character of one of the more 

 highly organized of the rotiferous class of Infusoria, hitherto sup- 

 posed to be androgenous. This discovery was first made by obser- 

 ving the difference in the form and development of the embryo 

 while still enclosed in the ovisac of the parent animal. From the 

 extreme transparency of this form of rotifer, it is possible to trace 

 the progressive development of the young from theGrasffian vesicle 

 in the ovary to the period of mature gestation, when the embryo is 



