158 PHILOSOPHICAL TRANSACTIONS. [aNNO 1751. 



coral out of this water ; or even if you do but touch it in the water, the polypus 

 immediately retires into its cellule. In retiring, it contracts itself, the trough is 

 closed up (fig. 10, n, o) and each ray, (fig. 13, c) as also each appendix (a, a, a, a) 

 shrinks, and enters into itself, just as snails pull in their horns : cash ray pulls 

 in about half its length, and with their ends they adapt themselves to the edges 

 of the trough (fig. 14, 15). 



It is in this position that the polypus is seen the moment the coral is drawn 

 out of the sea. The polypus, in this contracted state, seen without a micro- 

 scope, resembles a drop of milk ; and this is what all the good coral-fishers take 

 for the real milk of the coral ; the rather because, by pressing the bark of the 

 coral with the fingers, the polypus is forced out, and in coming forth it always 

 retains the appearance of milk. And this makes it probable, that the accurate 

 Andreas Caesalpinus, who was the first observer of milk in coral, in reality saw 

 nothing but the polypi in the semblance of milk. 



Though the polypi have their belly (fig. 12, g) quite disengaged from the cel- 

 lule, as said above; yet they always keep it therein, shortening and widening it 

 so, as to make it thicker than the mouth or opening of the cellule (fig. 1 6, g) : 

 and this may be seen very distinctly by separating the cellule and its polypus 

 from the substance of the coral, and then observing it on the back part. In this 

 attitude it is that we see, not only the belly very much shortened (fig. 1 6, g) but 

 also the position in which the polypus keeps itself in its own habitation. 



At the bottom of the belly (fig. 12, g) of some polypi, are observed some 

 roundish hydatides, extremely small and soft, transparent, yellowish, or tending 

 to pale. The situation and figure of these hydatids induced Dr. D. to believe, 

 that they are true eggs of the polypus. Although the size of these eggs is not 

 much above the 40th part of a line, yet by the assistance of a good microscope, 

 are discovered some vestiges of little grains, like those which are common on the 

 bark and substance of coral. These eggs are detached from the polypus, and 

 being soft they adapt themselves, and stick to the hard bodies, on which they 

 all. Afterwards they spread at the foot or bottom, and swell up a little (fig. 17) ; 

 and in this case we very well discern an inward cavity in them, the upper part of 

 which becomes uneven by 8 wrinkles, (fig. 18) but is not open as yet. Shut up 

 within this cavity the fetus of the polypus remains, contracted within itself, and as it 

 were without form. In due time the polypus grows ripe, and as it were adult ; 

 and the upper part (fig. 1 , s, t, s) opening, it comes forth properly extended (fig. 

 12, g), and thus furnishes the coral with nutriment. 



While the first cellule is shut up, (fig. 17) or the egg of the coral is in its 

 substance, we do not find any one hard part in it like bone or marble ; it is all 

 soft : but afterwards, when the cellule opens, we begin to observe some hard 

 lamellae ; and when it is grown larger, and arrived at the height of about a line 



