458 Royal Society. 



the epoch affect, first, the semimenstrual inequality; secondly, 

 the parallax correction of the time ; thirdly, the declination correc- 

 tion of the times ; fourthly, the parallax correction of heights ; and 

 fifthly, the declination correction of the heights? 3. Does the pa- 

 rallax corrections of height vary as the parallax ? 4. Does the pa- 

 rallax correction of time vary as the parallax ? 5, Does the declina- 

 tion correction of the heights vary as the square of the declination ? 

 6. Does the declination correction of time vary as the square of the 

 declination ? 7. Can the laws of the corrections be deduced from 

 a single year ? 8. Are there any regular differences betvi^een the 

 corrections of successive years ? 9. Do the corrections at different 

 places agree in themselves ? It does not appear that any change 

 of the epoch will produce an accordance of the observed laws with 

 the theory, some of the inequalities requiring one epoch for this 

 purpose, and some requiring another. The inequalities in different 

 years and different places are also compared. 



Mr. Whewell remarks, that since it has now been shown that 

 good tide tables may be obtained from short series of observations, 

 his researches with regard to the determination of the lunar correc- 

 tions may be concluded ; and the proper mode of farther prosecuting 

 the subject, would be to have tide observations at several stations, 

 each observatory reducing its own observations, and thus constantly 

 improving the tables, as is practised in other branches of Astro- 

 nomy. 



" Researches in Embryology." First Series. By Martin Barry, 

 M.D., F.R.S.E., Fellow of the Royal College of Physicians in Edin- 

 burgh. Communicated by P. M. Roget, M.D., Sec. R.S. 



This paper is divided into two parts. In the first part the author 

 describes the origin and structure of the ovisac, a vesicle common 

 to all vertebrated animals, but hitherto regarded as the inner mem- 

 brane of the "folliculus Graafianus " in Mammalia, and by some 

 authors denominated the " chorion " in other Vertebrata. He also 

 describes the real nature of the " folliculus Graafianus," and its re- 

 lation to the calyx of the Bird ; the germinal vesicle and its con- 

 tents, as being the most primitive portion of the ovum ; the order of 

 formation of the several other parts of the ovarian ovum ; and the 

 true chorion of Mammalia as being a structure superadded within 

 the ovary. 



In the second part the author describes a granulous tunic of the 

 ovum of Mammalia not hitherto observed ; the manner of origin 

 of the " membrana granulosa" of authors ; the different situations of 

 the ovum in the Graafian vesicle at certain periods ante coitum, not 

 hitherto observed ; and certain structures by means of which the 

 ovum is made to occupy these several situations. 



The following are the principal facts made known by Dr. Barry 

 in this memoir ; but other facts are also mentioned, which he in- 

 tends to make the subject of a future communication. In Mammalia 

 and in Birds the germinal vesicle and its contents are those parts 

 of the ovum which are first formed. The germinal vesicle at an 

 early period is surrounded by peculiar granules, forming an envelope 



