POST-LARVAL, FIXED OR SPAT STAGES 55 



parts of the bay. This is about six miles from the station but daily visits 

 were made, the strips of glass were one by one withdrawn and examined 

 with a lens, and, whenever a suspicious looking speck was observed, the 

 glass was put into a pail of sea-water and taken to the station to be 

 examined with a compound microscope. 



The glass strips were not too big to be used on the stage of a micro- 

 scope, either side could be equally well examined, either reflected or trans- 

 mitted light used. In the crocks they soon become dirty, receiving a slimy 

 coat speckled with sediment, plants and animals. Standing the strips 

 vertically in the crocks minimizes the amount of sediment that clings to 

 them, and a smart sweep through the water, when removing them, washes 

 away a good deal of that deposited, without carrying away spat, which 

 are too firmly fixed. The method has a broad application. There are 

 bacteria, diatoms, algse, protozoa, sponges, hydroids, polyzoa, worms, 

 crustaceans, snails, bivalves, and other forms caught, either attached, 

 clinging to or creeping over the surface. It seemed as if everything but 

 oysters could be obtained. This went on for some time. So far as I 

 could see I had neglected nothing. Could it be that there were no oyster 

 larva? in the water? My work on bivalve larvae, which I had been pur- 

 suing side by side with these experiments, had already singled out a par- 

 ticular larva of a different appearance from all the rest, that had been in- 

 creasing in abundance, but whether it was an oyster or not depended upon 

 whether it could be caught on the glass and recognized as an oyster-spat. 



At length, on the 16th of August, I discovered a single minute oyster- 

 spat, bearing unmistakable marks of recognition, and displaying both the 

 now familiar larval shell (prodissoconch) of the plankton and the surround- 

 ing lately deposited thin rim of spat shell (dissoconch). On the 19th I found 

 a second, and on the 22nd a third. Everything speedily became clear. 

 My experiments had been running ahead of nature, a circumstance which, 

 of course, I could not have known before hand. Oyster larvae had been 

 in the water, but they were not ready to become fixed and transformed 

 into spat. They had to bide their time. This, as will be readilv ad- 

 mitted, is a very important point to the oyster culturist, for there is no use 

 expecting results until the proper time arrives. I had caught a few of 

 the very first spat of the season. The small ones obtained earlier in the 

 summer were belated specimens of the previous year, which explains 

 their scarcity and the fact that I could not find smaller ones. 



Attachment to Natural Marine Objects. — After reaching this con- 

 clusion I again turned to the examination of natural marine objects, and 

 on the 2nd of September found a spat on the surface of a half grown 

 oyster shell. From this time onwards they were found in increasing 

 numbers and on various objects — shells of the oyster, mussel, clam, 

 quahaug, bar-clam, razor-clam, round whelk and stones, but they must 

 occur on many other objects as well. Judging from the numbers of half- 



