No. 522] 



THE CANADIAN OYSTER 



347 



one withdrawn and examined with a lens, and whenever 

 a suspicious looking speck was observed the glass was 

 put in a pail of sea-water and taken to the station to be 

 examined with a compound microscope. 



The strips soon became dirty, receiving a slimy coat 

 speckled with sediment, plants and animals. There were 

 bacteria, diatoms, algae, protozoa, sponge-spicules, hy- 

 droids, polyzoon-colonies, worm-larva?, crustacean larvae, 

 small snails, etc. It seemed as if everything but oysters 

 could be obtained. So far as I saw, I had neglected noth- 

 ing that might contribute to the result in view. Could it 

 be that my suspected larva? were not oysters, that there 

 were no oyster larvae or oyster eggs in the water ! Once 

 more I was bewildered. 



At length, on the sixteenth of August, I discovered a 

 single minute oyster spat, bearing unmi>takal>le marks 

 of recognition ami enclosing within the lately deposited 

 spat-shell the prodissoconch of the free-swimming larva. 

 On the nineteenth I found a second (Fig. >V). and on the 

 twenty-second a third (Fig. 1). Everything speedily be- 

 came clear. My experiments had been running ahead 

 of nature. Oyster larvae had been in the water, but they 

 were not ready to transform into spat. They had to 

 wait their time. On the thirty-first of August a fourth 

 was taken. 



After finding the first oyster-spat on glass I at once 

 directed increased attention to natural marine objects 

 and on the second of September I found a spat on the 

 surface of a half -grown oyster-shell. From this time for- 

 wards they were to be found in increasing numbers and 

 on various objects and, after being once shown them, the 

 deck-hands of the steamer Ostrea could also find them. 

 I have found spat on the shells of the oyster, mussel, clam, 

 quohog, bar-clam, razor-clam, round whelk and on stones, 

 but they must occur on many other objects as well. Judg- 

 ing from the numbers of half-grown oysters that carry 

 periwinkle-shells at their umbos, it would seem that the 

 periwinkle is a common base of fixation, although I did 



