324 ANIMAL REPRODUCTIONS. 
zani has given fome inftances in his Pradromo, 
and after him, I have mentioned them in Ja Pa- 
lingenefie, part 9 ; the reader is referred to thefe 
two works, for I fhould here confine myfelf to 
my own obfervations. | : 
A profile of the anterior part of a {nail deca- 
pitated 8 May, and delineated 21 June, is~a lit- 
ile magnified, fig. 4. The two large horns, g, g, 
are beginning to protrude ; the left is further ad- 
vanced than the right, which is juft originating. 
A brown, or blackifh line proceeds from the large 
right horn; this is the optic nerve and its muf- 
cle; the various motions and ftructure of which, 
Swammerdam has difplayed to our admiration, 
Some tranfparency is perceptible in the fiefh ; and, 
as it increafes greatly in {nails that have abftain- — 
ed a month or two from food, the optic nerve 
and mufcle become much more evident. <A 
white line /, runs along the back; but I am 
ignorant whether it is a veflel, The anterior 
part of the fame {nail, yiewed from before, is re- 
prefented from the life, fig. 5: only the upper 
extremity of the large horns is feen, and at the 
extremity there appears a minute black point ; 
this is the eye of the {nail, in which Swammer- 
dam aflures us he has found the three humours 
of an eye, the two tunics, the uvea, and arach- 
noid. Here the eye is already vifible; though — 
the horn is but in its origin, it is perceptible in 
thofe 
