On the Progress of Embryology in the Year 1840. 337 



to my memory the very similar words which I used when I 

 first announced the invention of the polarizing microscope in 

 your Journal (vol. v. p. 324), viz. 



" The field of view appears scattered with the most brilliant 

 assemblage of highly coloured gems, affording one of the 

 most pleasing sights that can be imagined. The darkness of 

 the ground on which they display themselves greatly en- 

 hances the effect." 



With regard to the above points, then, I consider that they 

 were sufficiently established by me in 1836. 



The second part of Mr. Warington's paper, however, con- 

 tains a fact both new and important ; I mean the solution of 

 the yellow crystals in the liquid and the formation of the red 

 ones, of a different form, in their places. But this observa- 

 tion is most strictly analogous to the phenomenon which I 

 discovered in the iodide of lead, and published in your Journal 

 (vol. ix. p + 405), viz. the sudden change of a crystal of that 

 salt from the form of a white needle to that of a row of thin 

 yellow regular hexagons lying in a straight line. Such a me- 

 tamorphosis was previously unexampled ; Mr.Warington has 

 now furnished us with a second example (also the iodide of 

 a metal) : I have myself observed something similar in the 

 iodide of tin ; and I recommend the whole subject of the cry- 

 stalline form of the metallic iodides to the renewed and care- 

 ful consideration of chemists. 



I am glad of the opportunity afforded me by Mr. Waring- 

 ton's paper of again calling attention to these very curious 

 facts, which appear to me to open a path that promises to lead 

 far into those arcana of Nature, the mysteries of molecular 

 action. 



I remain, Gentlemen, yours, &c, 



London, Oct. 1, 1842. H. F. TALBOT. 



LVIII. On the Progress of Embryology in the Year 1S40*. 



" COME interesting discoveries rendered the past year a 

 highly productive one for embryology. Two main pro- 

 blems which engaged the various physiologists here occupy 

 the foreground, namely, the earliest development of the Mam r 

 malia, and the metamorphoses of the germinal membrane in its 

 transformation into the embryo******. So long as the meta- 

 morphoses of the germinal vesicle following fecundation could 

 be considered only hypothetically, it was assumed that the Pur- 

 kinjean [germinal] vesicle either burst and poured out its con- 

 tents, or became flattened ; and now contributed to the forma- 



* From Professor Valentin's Report in the Repertorium fur Anatomie 

 und PJjysiologie, Jahrgang 1841. 



