402 Proceedings of the 



themselves to new localities. During the day I have only 

 seen on one occasion an oyster form a new byssus. This noc- 

 turnal habit is doubtless instinctive precaution ; for, should 

 oysters move during the day, they are more likely to become 

 the food of fishes and other animals which prey upon them. 

 Their movements are instinctive, and guided by the sense of 

 touch. Darkness suits them better than daylight, of the dif- 

 ference of which they are very sensitive. Most of the oysters 

 in which I have found pearls had external marks of having 

 been retarded in their lateral growth, and displaced in early 

 life from their fixed position on a bank. I am inclined to 

 believe that oysters which have abundance of food, and are 

 not disturbed, remain fixed for the last two or three years of 

 their growth to one spot. These are less likely to have a 

 large proportion of pearl-bearing individuals among them. 

 This of course requires more extensive practical observation, 

 either on the beds in the harbour of Trincomalie, or on the 

 pearl banks of Arrippo. With reference to the formation of 

 pearls, I have nothing new to add to the accounts found in 

 the best modern books on the subject, except that one which 

 modifies the view taken by SirE. Home, — viz., that pearls are 

 formed from abortive ova. I believe the ova left behind in 

 the ovaria are not the nuclei of pearls, but that the ova which 

 escape through the extended coats of an overgrown ovarium, 

 and are imbedded in the interstices of the mantle, become nu- 

 clei of pearls formed in this situation. I have repeatedly ex- 

 amined seed, or young pearls, in process of formation ; and, 

 with a magnifying power of 15 inch lens, I was able to 

 see distinctly the outlines of two and three ova, through 

 the first or superficial layer of nacre, surrounded by groups 

 of ova. It can be readily understood how an overcharged ova- 

 rium will, by some accident or spontaneous evolution, have its 

 coats ruptured, allowing the ova to escape, and become inserted 

 in the contiguous attenuated parts of the mantle. As pearls 

 are more usually found imbedded in the mantle near the hinge, 

 — the most likely place where the ovarium is liable to rup- 

 ture, — I consider this very conclusive of the new theory I have 

 here proposed, I may also observe, that I have seen the ves- 

 tiges or cicatrices in the mantle where the pearls once existed. 



