CONTINENTAL OYSTER CULTURE. 373 



have been observed heavy with spat, the brood has been emitted, 

 collectors laid around, and yet scarcely a trace of deposit has 

 been found. Whether, under the conditions favourable to artifi- 

 cial rearing, the spat is not properly fertilized, or the brood are 

 born too feeble to survive, or are deficient in the secretion by 

 which they adhere, or are otherwise wanting, is hard to say ; but 

 the fact remains that the mixture of salt and fresh water, that is 

 most favourable to rapid growth and development, is apparently 

 fatal to successful reproduction. 



This fact narrows the choice of a situation for a breeding- 

 ground, but the selection is further restricted by a condition that 

 every locality suitable for successful reproduction must satisfy, i.e., 

 it should be near a rearing-ground. When first they adhere to 

 the collecters, the young Oysters are very small and delicate. 

 Now for several practical reasons the collectors should rarely be 

 left on the spatting-ground for more than two, three, or at most 

 four months. Hence the young Oysters have to be moved at a 

 critical age, and if the rearing-ground be not near at hand, the 

 mortality is likely to be heavy. It is only when the Oysters have 

 attained a diameter of lj to If in. that they can be safely carried 

 to a distance. A salinity of sea- water, and contiguity to a rearing- 

 ground therefore are two conditions of aptitude for breeding pur- 

 poses ; but in selecting a breeding-ground there are also some physi- 

 cal signs by which suitability may be further recognised. The most 

 unmistakeable sign of all is, the existence of an Oyster-bed. But 

 even where this is wanting, the presence of Oysters, especially if 

 they are numerous, is a sure indication of aptitude. Yet the 

 absence of Oysters is not a positive proof of inaptitude for 

 breeding purposes, for in many very suitable places this absence 

 has been traced to the deficiency of solid bodies on which the 

 brood could collect. Not unfrequently where Oysters were 

 scarce, the construction of a breakwater, or stonework, has sufficed 

 to make them numerous. Spezia and Venice may be cited as 

 instances. Another, and to some extent satisfactory indication of 

 fitness, or the reverse, is the nature of the bottom. A clear, 

 clean, and homogeneous mud, like clay, appears to be very suit- 

 able, and it is a favourable indication if the calcareous tubes of 

 Serpulce (vermi anellidi tubicoli) are found adhering to any 

 submerged body. Grounds covered with algae and Zostera (sea- 

 wrack) are to be avoided, as also those of quartz sand, especially 



