VOL. v.] PHILOSOPHICAL TRANSACTIONS. 443 



membrane, chorion; then, that portion of the string, wherein the laxness, 

 inequalities, and con torsions of the membrane, together with all the contained 

 vessels in their proper situation, are observed; next, the macula, appearing 

 somewhat prominent in one of the arteries, by which may easily be found the 

 passage of the blood to the placenta, and its difficult regress towards the navel 

 of the foetus ; moreover, the interior substance of the placenta, and all the 

 ramifications of the veins and arteries. 



Secondly, in a male foetus, a review of all the former particulars, together 

 with several differences from that of the female. 



To these observations is subjoined a collection of letters, written by this 

 author to divers learned men, touching generation, with their answers. 



III. Joh. Ludov. Gansii, M.D.Coralliorum Historia. Francofurti, 1669. 12mo. 



In this history the author affirms to have digested both what has been de- 

 livered of corals, and what himself has observed and tried of that curious pro- 

 duct of nature. His opinion is, that coral is formed out of a glutinous juice, 

 which being turned into stone by a salt, abounding in it, rises up in the form 

 of a shrub ; the salt being the cause that makes plants spread into branches.* 

 The places of the production of coral he names to be the Red Sea, the Per- 

 sian Gulf, the Sicilian and Neapolitan shore. Some of them are red, others 

 white, others blackish. To this account he annexes various preparations made 

 of them : as also divers solutions, of which he delivers one as an excellent 

 dissolvent both of corals and pearls, made of very well rectified spirit of salt, 

 digested and freed of its coiTosiveness, and then mixed with good spirit of 

 wine distilled and brought over the alembic. 



The Answer of Mons. Mariotte to Mons. Pecquet, concealing the 

 Opinion, that the Choroides is the Principal Organ of Sight. 

 iV» 59, p- 1023. 



Sir, — I have in your answer ^ seen the reasons which hinder you from be- 

 lieving that the choroides is the principal organ of sight; but though they 

 were very acute, and carried a great deal of probability with them, yet I did 

 not find them strong enough to oblige me to grant back again this pre- 

 eminence to the retina. 



You say in your first objection, that if the sclerotis and the choroides be 

 taken away from an eye that is very fresh, and the retina be left distended on 



* This explanation of the formation of corals is very unsatisfactory. It is now known that coral- 

 branches are the habitations of a peculiar tribe of polypous animals or zoophytes, and that the growth 

 of these branches keeps pace with the growth and multiplication of the inhabiting animals. 



f See No. 35, p. 243, &c. of this volume. 



3 K 2 



