XXV -THE METAMORPHOSIS AND POST-LARVAL STAGES OF 

 DEVELOPMENT OF THE OYSTER. 



By John A. Eyder. 



Professor Brooks in his elaborate paper on the development of this 

 mollusk, in the report for 1880 of the commissioners of fisheries of Mary- 

 land, page 25, observes, in relation to the oldest embryos figured by him 

 (Figs. 44 and 45, Plate VI) : " The American oyster reaches this stage 

 in from twenty-four hours to six days after the egg is fertilized, the 

 rate of development being determined mainly by the temperature of 

 the water." He further states, "All my attempts to get later stages 

 than these failed through my inability to find any way to change the 

 water without losing the young oyster, and I am therefore unable to 

 describe the manner in which the swimming embryo becomes converted 

 into the adult, but I hope that this gap will be filled either by future 

 observations of my own or by those of some other embryologist." These 

 remarks applied to the American oyster, Ostrea virginica. Since then 

 Prof. H. J. Eice has described what he has called the proboscis stage of 

 development of the embryo oyster, said to be assumed after the oldest 

 stages figured by Brooks have been passed over. This stage the writer 

 has never seen, or if it was observed, he has failed to note what has 

 been found by Eice. 



The embryo European oyster, 0. eduUs, has been discussed by Pro- 

 fessor Huxley,* and his remarks upon the manner of its metamorphosis, 

 on account of their clearness, I take the liberty of reproducing here with 

 some slight verbal changes; I have also borrowed one of his figures in 

 order to make his language more easily intelligible. His remarks are 

 as follows : 



" The young animal which is hatched out of the egg of the oyster is 

 extremely unlike the adult, and it will be worth while to consider its 

 character more closely than we have hitherto done. 



" Under a tolerably high magnifying power the body is observed to 

 be inclosed in a transparent, but rather thick shell (Fig. 1, L), com- 

 posed, as in the parent, of two valves united by a straight hinge, h. 

 But these valves are symmetrical and similar in size and shape, so that 

 the shell resembles that of a cockle more than it does that of an adult 



* In a lecture delivered at the Koyal Institution, Friday, May 11, 1883. Published 

 in full in the English Illustrated Magazine for October and November, 1883, pp. 47- 

 55 and 112-121. 



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