LARVAL OYSTEES. 727 



who has claimed that he had succeeded in rearing them to the age of five months, specimens of 

 which it is said were shown at the Fishery Exhibition recently held in Edinburgh. 



Experiments at Saint Jerome's Ceeek. — Our experiments made at Saint Jerome's Greek 

 during the past summer gave the most contradictory results, and the interval of development 

 between that of our oldest embryo with its diminutive Pisidium like valves measuring about g^ 

 inch in diameter, and that of the embryo when its valves first begin to lose their embryonic form, 

 still remains unbridged. The dimensions of the embryo or "fry," as we may more properly call it 

 when it becomes fixed, are between ^^ and -^ inch according as the measurement is made longi- 

 tudinally or transversely. The difference in magnitude between the oldest artificially incubated 

 fry seen by me and that of the youngest fixed embryos which I collected is very small, amounting 

 only to ^^00 inch, or a little more than ^^ inch. To determine the relative volumes of these 

 stages, and consequently the amount of food which has been taken in and converted into the 

 structure of the more advanced stage in addition to the original bulk of the egg, we need only 

 take the cubes of their respective diameters and compare them. Taking the diameter of the egg, 

 or j^ inch, as the diameter of the most advanced embryo seen by me, which we will consider 

 unity, and comparing it with ^ inch, or the transverse diameter of the newly fixed fry, we find, 

 after having reduced the last quantity to its simplest form as compared with 1, or the diameter of 

 the egg, that we have 5.1+. The diameters then of the first and last embryonic or truly larval 

 stages are to each other as 1 is to 5.1+ , and consequently their volumes will be to each other as 

 the cubes of these numbers, or as 1 is to 132.651 +. The difference between these two quantities, 

 or 131.651+ times 1, will give us approximately the amount of food material which has been taken 

 up by the embryo in passing from the condition when it was first able to feed until it fixed itself, 

 showing that the process of growth has been going on vigorously in order to augment the volume 

 of the young creature at the enormous rate indicated by our figures. We have, however, been 

 dealing not with absolute but with relative or compared volumes only; if the egg contains 

 TsTo ooooo cubic inch of protoplasmic matter approximately, the newly-fixed fry, which we will 

 assume to be globular, and contains, as shown above, over 132 times as much material, the 

 absolute bulk of the latter will be sfowoooo cubic inch multiplied by 132, or 2 rooowor cubic 

 inch, which, in its simplest form, is therefore 1-92 aoro cubic inch, or. the absolute volume of the 

 newly fixed fry. Ninety cubed, or 729,000 young Oysters could therefore be contained in a cubic 

 inch of space, if taken at the stage at which they begin to be transformed into spat. This large 

 number is, of course, small when compared with 125,000,000, the number of eggs which might be 

 contained by the same extent of space. 



The larval character of the young Oyster. — The proof of the larval character of 

 the youngest fixed stage of the Oyster rests upon the three following well-ascertained facts: 

 Ist. The perfect symmetry and great convexity of the valves; 2d. The entirely different shape 

 of the shell as compared with those of the spat and adult; 3d. Its wholly different micro- 

 scopic structure when compared with the later and full-grown stages. The form of the shell, at 

 the time the animal is about to begin to develop the spat shell, is suborbicular, very thin, ven- 

 tricose, resembling in many respects the shell of Gyclas or Pisidium, having the symmetry of 

 those genera, with umbones of about the same form and prominence. These features mark the 

 larval shell of the Oyster so unmistakably that its valves may always be very readily recognized 

 at the tips of the valves of spat under a year old. The larval valves lie on the tips of the valves 

 of the spat like small hemispherical caps, but can usually not be found after the young Oyster 

 enters upon its second year, as its umbones, together with the larval shells which surmount them, 



