74 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



grains proceed to their perfection. In the fucus vesiculosus this change of colour 

 and consistency in the mucus is evident to common sight. It is still more evident 

 in the fucus selaginoideus, where the temporary bright and vivid colour of the mu- 

 cus, followed by a prompt decay after that period, has struck even those naturalists 

 who most decidedly opposed the existence of male parts in these plants ; and I am 

 confident, from the steadiness with which nature adheres to her general plans, that 

 proper observations will demonstrate the same in every species of those submersed 

 algae, and confirm what the forementioned analogies induce me to think, viz. That 

 the vesicles of all these plants, whatever be their shape, if containing grains and 

 mucus, are to be considered as hermaphrodite flowers ; the grains they contain as 

 their seeds, and the mucous substance as their pollen. 



END OF THE EIGHTY-SIXTH VOLUME OF THE ORIGINAL. 



/. The Croonian Lecture. In which some of the Morbid Actions of the Straight 

 Muscles and Cornea of the Eye are explained, and their Treatment considered. 

 By Everard Home, Esq. f. r. s. Anno 1797. Vol. lxxxvii. p. l, 



In my 2 former Lectures, to the r. s. on Vision, I confined myself to the adjust- 

 ment of the eye for seeing objects at different distances. From the attention which 

 I there necessarily paid to the natural actions of the muscles, and the structure of 

 the cornea, I have been led to consider the effects which a diseased state of these 

 parts will produce on the phenomena of vision. 



That I may be understood in giving an account of the diseases that arise from 

 morbid actions of the straight muscles of the eye, it will be necessary to explain the 

 effects which their natural actions are intended to produce ; for these are not con- 

 fined to the separate, or combined actions of the muscles, but also vary according 

 to the degree of their contraction. The first and most simple of these effects is that 

 of moving the eye-balls in different directions. The 2d is that of making the mo- 

 tions of the 2 eyes correspond with such a degree of accuracy, that when an object 

 is viewed with both eyes, the impressions from the object shall be made on cor- 

 responding parts of the retina of each eye. The 3d is that of compressing the eye- 

 balls laterally, which renders the cornea more convex, and pushes forwards the 

 crystalline lens, to adjust the eye to near distances. Distinct vision with 2 eyes de- 

 pends upon these different actions of the straight muscles ; an imperfection in any 

 one of them, as it renders the organ unfit to perform its functions, must be con- 

 sidered as a disease. Three different diseases occur in practice, which appear to 

 arise from morbid actions of the straight muscles. These are, an inability to see 

 near objects distinctly ; double vision ; and squinting. I shall consider each of 

 these separately. 



Of the inability to see near objects distinctly. — As that action of the muscles 

 which produces the adjustment of the eye to near objects, consists of the greatest 



