17(5 



the source of the lime, though he by no means intends to assert the 

 impossibility of its being derived from the shell. 



On the Placenta. By Sir Everard Home, Bart. V.P.R.S. Read 

 June 27, 1822. [Phil. Trans. 1822,^. 401.] 



After adverting to the discovery of the unattached human ovum 

 in the uterus, and to the formation of the placenta independent of 

 the chorion, the author proceeds to show that the office of the pla- 

 centa, and when that is wanting, of the chorion, being to supply ma- 

 terials for the growth of the embryo, it varies in structure, and has 

 a peculiar form in every genus of animal, and is to be considered as 

 the means employed by Nature to prevent the whole system respect- 

 ing animals from being thrown into confusion by any two different 

 genera continuing to interbreed with one another, and which cannot 

 take place without a new form of placenta is employed, for which 

 there is no provision. The author then states that the period of 

 utero- gestation depends upon the structure of the placenta or cho- 

 rion ; that where they are very vascular it will be short, and where 

 the reverse very long ; and that where the female of one species 

 breeds from the male of another, whose utero-gestation is different, 

 the hybrid is brought forth at the end of the longest period of the 

 utero-gestation of the species concerned. Sir Everard thinks that 

 the placenta and chorion are instrumental in producing the stimulus, 

 in consequence of which parturition comes on ; for as soon as double 

 circulation takes place in the foetus, which is not till the lungs are 

 perfected, the placenta is so much diminished, that this alone may 

 produce a separation of the placenta and chorion, and expulsion of 

 the young. The author concludes this paper with a specimen of a 

 new classification of animals, founded upon the variation of struc- 

 ture of the placenta, of which the first class only is given, including 

 animals in which the ovum becomes attached to the womb of the 

 mother. This class comprises seven orders, distinguished by pecu- 

 liarities in the structure of the chorion and placenta. 



Of the Geographical Situation of the Three Presidencies, Calcutta, 

 Madras, and Bombay, in the East Indies. By J. Goldingham, Esq. 

 F.R.S. Read June 27, 1822. [Phil. Trans. 1822, p. 408.] 



From an extended series of observations of the eclipses of Jupiter's 

 satellites, corrected for the difference of the tables from the obser- 

 vations taken at Greenwich, at or about the time of each eclipse, 

 the mean longitude of the Observatory at Madras is 80 17' 21" E,, 

 and the mean latitude found by meridional observations of the sun 

 and stars north and south of zenith, taken with the sextant, circular 

 instrument, and zenith sector, is 13 4' 9" N. 



By a series of corresponding eclipses of Jupiter's satellites, taken 

 at Fort William, the longitude of the Fort appears to be 88 23' 

 39" E. 



