February 23, 18S3.] 



SCIENCE. 



61 



troduced by the -writer for extracting the eggs 

 and milt from the adults for spawning pur- 

 poses. This consisted in applying essentially 

 the same method for the extraction of the eggs 

 as is used in spawning fish artificiallj' ; therebj' 

 avoiding the admixture Of foreign matters, and 

 fragments of the other tissues of the animal, 

 such as occurs when the ovary is cut out, and 

 chopped up into fragments in water. A very 

 little experience will enable a person to find 

 the ovary or spermary on the sides of the body 

 of the animal when one valve is removed. 

 Removing the mantle below and in front of 

 the heart-chamber, its principal ducts will" be 

 exposed ; and these may be traced backwards 

 on either side of the ventral process of the 

 bod3"-mass to below the muscle, where the pro- 

 cess juts into the snprabranchial chamber with 

 its apex reacliing to the commencement of the 

 cloaca. When the spawn is abundant, the 

 ducts are usually gorged, and look like prom- 

 inent veins distended with a creamy substance. 



To remove the generative products without 

 cutting or lacerating the rej^roductive organs, 

 one should be provided with a medicine-drop- 

 per or short pipette with a curved tip and a 

 compressible rubber bulb at top. With the 

 curved point of the pipette, the ducts of the re- 

 productive organ are gently and flrmlj' stroked 

 in the direction of the external opening from 

 before backwards. This, if properly done, will 

 force out the eggs or the milt in a stream from 

 the genital opening of the same side ; when the 

 pipette may he applied to suck up the extruded 

 spawn, and drop it into water without the ad- 

 mixture of any deleterious foreign matters 

 whatever. If the soft parts of the oyster have 

 been left attached to the one valve, which I 

 have found to be most convenient in practice, 

 the other side of the animal may be treated in 

 the same way, as the reproductive organ has 

 an opening on either side of the bodj'. To do 

 this the head end of the animal, next the hinge, 

 is simply thrown back over the adductor, the 

 mantle cut open, and the spawn pressed out 

 of the ducts of the under side as before. 



By the foregoing method, which is much 

 neater and more cleanly than any other, the 

 best spawn is obtained ; and it is often pos- 

 sible to impregnate fullj' ninetj- per cent of 

 the eggs taken. When eggs so treated are 

 placed under the microscope, comparatively 

 > few injured ones will he observed ; at any rate, 

 the result will be vastlj^ more satisfactory' than 

 if the animal is crushed or chopped up in order 

 to get the spawn. Many billions of eggs might 

 be fertilized in a day by this plan. 



As a result of the experience with the fixa- 



tion of the embryos resulting from the artifi- 

 cially fertiHzed eggs, as described at the 

 outset, it was determined to investigate the 

 mode of fixation to learn if there was any 

 uniformity about it. I now believe that the 

 fixation of the fry is accomplished by the 

 border of the larval mantle, the existence of 

 byssal organs being doubtful. The oldest 

 larval shells of artificially reared embryos 

 have the hinges of the valves truncated and 

 without beaks or umbos ; while the fry on the 

 eve of conversion into spat has a distinct 

 beak to each of its valves, which projects ante- 

 riorly beyond the hinge-line. The" valves, at 

 this time, are verj' ventricose, quite symmet- 

 rical, and similar to Pisidium in form, or in 

 the most marked contrast, in respect of shape, 

 with the irregularity of the older spat and 

 adult. 



When a large number of very j'oung natural 

 spat is examined on their attachments, it will 

 be found, that in every case the apex of the 

 umbo of both the valves of the larval shell are 

 turned towards the left if the hinge end is 

 directed towards the north. It is therefore 

 clear, that when the j'oung attach themselves, 

 they do so constantly by one and invariably 

 the same side. Upon examining spat which 

 has just begun to form a shell}' attachment, 

 we find this to begin at the border of the larval 

 shell, and to grow outwards ; the hinge being 

 continued for a time laterally' or on a line 

 with that of the larval shell. We may also 

 note, that the distal free border of the lower 

 valve is the only part of the fry shell which 

 comes into direct contact with the object to 

 which attachment occurs ; and that the hinge 

 end of the larval or fry shell is directed some- 

 what upwards, the line of junction of the 

 valves having at first formed an angle of 

 nearly thirty degrees with the plane of the 

 surface to which fixation occurred. This con- 

 dition of things is so invariable that it may be 

 regarded as universal^ the case. How does 

 the fixation occur? A byssus at most would 

 onl}' serve for temporary anchorage ; and we 

 find, that as soon as the first calcareous depos- 

 its are formed to build the asj'mmetrical valves 

 of the spat, the lower valve of the latter is for 

 the first time glued down by the conchioHne 

 or periostracum covering it externally, and 

 that it often continues to be so affixed until it 

 is nearly two inches in diameter. After this 

 the lower valve of the spat becomes free, and 

 the free margin of the shell begins to be bent 

 upwards. The valves of the symmetrical try 

 are also laminar and homogeneous in micro- 

 scopic structure ; while the verj' first layers of 



