rroN TIIK i-\i H:\INI; OF OYSTERS. 757 



developed to tin 1 greatest extent during the winter when it may l>e said the Oyster is in the 

 lies! eondition as regards tlesli, it does not follow that this plumpness is due to fatty matters, but 

 father to a larger amount of protoplasm tilling up the mantle, palps, and body mass. 



Our sections of the specimen described above show some other singular features which cannot 

 be passed over in silence. The principal of these is the presence of thick-walled vessels in thu 

 ventral lobes ot the mantle. In life we lind branching vessels visible in the transparent mantle in 

 \ cry impoverished specimens, such as the one under discussion. These vessels may be followed to 

 what are apparently their ultimate ramifications and seem to end abruptly. It is these vessels 

 which become obscured when the animal acquires tlesh; they are, in fact, hidden in the thick 

 deposit of connective tissue laid down in the mantle. They are grayish or whitish in color as they 

 shimmer through the transparent external epithelial and connective tissue layers of the mantle 

 organ. They are also different in character from other vessels excavated in the connective tissue 

 of the mantle, and which disappear with the atrophy of the hitter's substance, just as we noticed 

 was the case with the vessels of the body mass. In a specimen as greatly impoverished us the one 

 under discussion, the thick-walled pallial vessels become very conspicuous in transverse sections. 

 They may not have the same function as the bloodvessels of the ordinary wall-less form found in 

 the connective tissue, from which type they may be at once distinguished by their thick, finely 

 cellular walls. 



The almost total atrophy of the mesenchyrac or jnesoblast during the spawning season is a 

 very remarkable fact, no less so than its regeneration. It appears, however, as far as I have been 

 able to learn from transverse sections of very small spat, one-eighth to one-sixteenth of an inch 

 in diameter, that the absence of a well -developed connective tissue deposit also characterizes the 

 soft parts of the young animal. Indeed, the liver follicles here are relatively few in number, 

 whereas they are very numerous in the adult. The follicles in the young also lie in immediate 

 contact with the mantle, resembling in this respect the spawn spent adults. This, for einbryolo- 

 gical reasons, ought to be so. We find, in fact, according to the unanimous testimony of observers, 

 that the mesoblast in the Oyster develops by the proliferation of cells from the outer and inner 

 layers into the segmentation or body cavity. Why, then, should it not be absorbed and regener- 

 ated in the same way in the adult f There seems to be no valid reason assignable why this should 

 not be so, if we look upon the mesenchyme with its vessels and areolar tissue and cavernous 

 spaces as having been primarily derived from the embryonic body cavity. 



The arrangement of the intestine as shown in sections of spat as small as that described 

 above is essentially the same as in the adult. The second bend of the intestine crosses the 

 gullet in the same way, but the double lateral longitudinal fold or tnduplicatiou is not so well 

 marked as in the intestine of the adult. The stomach is more nearly cylindrical and not so 

 ii -regular as in the adult. The contents of both the stomach and intestine show that diatoms 

 have formed a large proportion of the food of the young animal, in the sections of which, these 

 contents, in a number of my preparations, have been kept in situ. 



The sections of the soft parts may be very readily double stained so as to bring out the 

 tissues of the reproductive organs very distinctly. To effect this, 1 throw the section into a 

 solution of methyl green for a few minutes, then into magenta, when it will be found that 

 the green will dye only the reproductive tissues, leaving the others scarcely tinged, while the red 

 will stain the mantle, liver, and connective tissues, mapping out these parts so distinctly as to 

 make a really useful as well as beautiful preparation. 



Considerable care must be exercised in the preparation of the color solutions, so as not to 

 have them too intense. The sections should also be at once and quickly dehydrated or else the 



