50 



surround tlie millions of eggs matured by a single female, 

 that only the most trifling fraction ever develop as illus- 

 trated by the above ca]culation. The egg of the oyster 

 being exoeedingiy small and heavier than water, imme- 

 diately falls to the bottom ujjon being set free by the 

 parent. Should the bottom be oozy or composed of sedi- 

 ment its chances of development are meagre indeed. Ir- 

 recoverably buried, the eggs do not in all probability 

 have the chance to begin to develoj} at all. The chances 

 of impregnation are also reduced, because the male and 

 female oysters empty their generative products directly 

 into the surrounding water, whereby the likelihood of 

 the eggs meeting with the male cells becomes diminished. 

 AYhat with falling into the mud and what with a lessen- 

 ed chance of becoming impregnated, it is not unlikely 

 that Mobius' estimate is very- nearly correct, but the 

 American oyster whose yield of eggs is much greater, 

 not only on account of its larger size, but also because 

 the eggs are smaller than those of the European, has 

 probably still fewer chances of survival. " The vigorous 

 growth of small organisms on surfaces fitted for the at- 

 tachment of Toung oysters also tends to cause sediment 



« CD e 



to gather in such places in the interstices of the little 

 organic forest where the eggs of the oyster no doubt 

 often become entombed or smothered by the crowded 

 grow^th surrounding them. 



IXTERFEEEXCE OF OTHEK AXIMAL LIFE. 



We have called attention above to the probable inter- 

 ference of small organic growths to the fixation of the 

 young fry ; in practice it is found that the larger organic 

 growths which establish themselvos on the collectors, al- 

 so become injurious. The two most conspicuous types 

 are the sessile Ascidians or tunicates and the barnacles. 

 I have frequently found fully one-half of the surface of a 



*Accordins: to estimates which I have made based on the fgures of the eggs of Oitrea edulis 

 given byM. Davaine, they are r-130 of an inch in diameter. Estimates based on the figures of 

 LacazeDuthiers give 1-270 of an inch, while M' bins estimates the size of the yourg fry at 1-156 

 of an inch. 



