1883.] on Oysters and the Oyster Question. 345 



pulsion. When this propeller is moderately active, the larvas dance 

 up and down in the water, with the disk uppermost ; but when 

 the action is more rapid, they swim horizontally with the disk 

 forward. 



How long the larval oysters remain in this locomotive state, under, 

 natural conditions, is unknown, but they may certainly retain their 

 activity for a week, as I have kept them myself in a bottle of sea- 

 water, which was neither changed nor aerated, for that period. But, 

 sooner or later, they settle down, fix themselves by one side to any 

 solid body, and rapidly take on the characters of minute oysters, 

 which have the appearance of flattened disks, -o^o*^ ^^ ^^ inch, more 

 or less, in diameter ; they are therefore perfectly visible, as white 

 dots, on the surface of the substance to which they adhere. In this 

 condition, the name of "spat" is also applied to them. The loco- 

 motive larvae being practically invisible in the sea, this spat appears to 

 be as it were precipitated out of the water ; and, since great quan- 

 tities appear at once, the oyster fishermen speak of a " fall " of spat. 



It is important to observe, that when oyster fishermen say that 

 there has been no " fall " of spat in a given season, all that is really 

 implied is that the young fixed oysters have not made their appearance. 

 The fact of the absence of a " fall of spat " does not justify the con- 

 clusion that the oysters have not bred as usual. It is quite possible, 

 that just as many eggs have been deposited in the branchial cavity, 

 and that just as many larvae have been set free as in other years ; but 

 that the larvae have been destroyed by those changes of temperature 

 to which they are so sensitive, or by other causes. But, of course, it 

 is also quite possible that the oysters have been really barren ; or 

 that, although the eggs have reached the mantle cavity, the larvae 

 have not hatched out. Oyster eggs, no less than hens' eggs, may be 

 addled. 



It is obviously useless to speculate upon the causes of a " failure 

 of spat," until, by the examination of samples of oysters from time to 

 time, and by sweeping the superjacent water with a fine towing-net, 

 the exact nature of the particular case of failure has been ascertained. 

 There is much reason to believe that the fertility of oysters preserved 

 in parks is greatly diminished, although the oysters themselves may 

 be improved in fatness and quality by the process, and that this is 

 especially the case when the water in which they are preserved has a 

 low degree of salinity ; and it is very desirable to ascertain the nature 

 of the modifications efi'ected in the structure and functions of the 

 reproductive apparatus of the oyster under these circumstances. 



It is unfortunate that the same word " spat " should be applied to 

 things so different in their nature, as the eggs and unhatched young 

 of the oyster contained within the mantle cavity on the one hand, and 

 the young fixed oysters on the other ; while there is no familiar name 

 for the very important stage of development which lies between these 

 two. " Brood," " fry," and " spat " would be very convenient names 

 for the three stages, if " brood " were not already in use for the 



