■1-38 lloijal Society. 



of a plane circle differs but little from that of a square having the 

 same area ; nor does it make any difference if the plates be turned 

 into cylinders, or prisms with any number of sides ; and the capacity 

 of a sphere or cylinder is the same as that of a plane equal to it in 

 superficial extent. 



The author proceeds to investigate some laws relating to the action 

 of electricity, when resulting from induction ; and particularly that 

 of the relation between electrical attraction and distance ; adducing 

 experiments in confirmation of the former being in the inverse dupli- 

 cate ratio of the latter. The attraction actually exhibited between 

 two equal spheres, he considers as composed of a system of parallel 

 forces, operating in right lines between the homologous points of the 

 opposed hemisphere. The author concludes by various observations 

 on the transmission of electricity to bodies in vacuo, from which he 

 infers the fallacy of all explanations of the phenomena of electrical 

 repulsion, founded on the supposed action of the atmosphere. 



The reading of a paper, entitled, "On the Generation of the Mar- 

 supial Animals ; with a Description of the impregnated Uterus of the 

 Kangaroo." By Richard Owen, Esq., Member and Assistant Conser- 

 vator of the Museum of the Royal College of Surgeons, London. 

 Communicated by Sir Anthony Carlisle, F.R.S. — was commenced. 



May ] . — Mr. Owen's paper was resumed, and concluded. 



The author gives a history of the opinions which have been ad- 

 vanced relative to the generative organs and functions of the Marsu- 

 piata, an extensive order of quadrupeds, including animals nourished 

 by every variety of food, and exercising very different powers of 

 progression, yet exhibiting a remarkable uniformity in their mode of 

 reproduction. In all the genera included in this family, the uterus 

 is double ; in most of them the vagina is also double ; and there is 

 always a single cloacal outlet for the excrementitious substances, and 

 the products of generation. There is a corresponding uniformity in 

 the male organs, which are bifurcated at the extremity, and have a 

 double groove for the transmission of the semen; and the male has 

 not only marsupial bones, similar to those of the female, but also 

 a muscle, similar to that which surrounds and compresses the mam- 

 mary gland in the female, winding round these bones like pulleys, 

 and acting as cremusters for the retraction and compression of the 

 testes. 



A minute description is then given of the results of the dissection 

 of the impregnated uterus of a kangaroo, which was obtained by Mr. 

 George Bennett, during a short residence in New South Wales, and 

 which, together with the impregnated uteri of the Ornithorhynchus 

 and other valuable specimens, were sent to the Museum of the Royal 

 College of Surgeons. The membrane corresponding to the chorion, or 

 external envelope of the foetus, was found not to have a vascular struc- 

 ture, and not to adhere in any part to the surface of the uterus ; 

 neither was there any appearance of a placental or of a villous struc- 

 ture. It adhered internally to a vascular membrane, into which the 

 umbilical stem of the foetus suddenly expanded, and which terminated 

 in a well-defined ridge, formed by the trunk of a terminal blood-vessel. 



