THE MICROSCOPE. 



rendered much more certain of getting its food with regularity, and 

 in sufficient abundance for its needs. 



The proboscis accordingly would represent one of those adapta- 

 tives for special purposes of organs to environment of which we find 

 so many examples in nature. The proboscis remains, as an acces- 

 sory food-gatherer, until the gills are of themselves capable of sup- 

 plying all the food necessary for the nutriment of the animal, when 

 it disappears, or rather is absorbed by the growth up around it, to 

 the solid portion of the body, which is made up principally of the 

 ovaries, or spermaries and liver. The size of the young oyster when 

 this disappearance takes place varies considerably. I have seen the 

 proboscis in animals all the way in diameter from ^ to i^j inches, 

 and again I have seen young oysters | of an inch in diameter, 

 which had passed through this stage entirely. The size seems to 

 depend largely upon the abundance of food upon the bed, those 

 having plenty of food growing very rapidly and accordingly much 

 larger before acquiring perfect gill-leaves than those upon beds or in 

 locations where food is scarce. While the proboscis is thus of great 

 value to the young oyster, in gathering food from the water as well 

 as taking from the ends of the gills that which has been gathered by 

 them, it is also of much importance to the adult, since the labial 

 palps, which grind the food in grooves at their bases, from the gills 

 to the mouth orifice, are entirely outgrowths and modifications of 

 the lip of our quondam acquaintance, the proboscis. I have not the 

 material at present time to represent all these changes which the lip 

 undergoes in being transformed into the palps, but such as I have 

 shows pretty clearly, in all except one point, the general process of 

 the transformations which take place. If one will examine with 

 some care the gills and labial, or mouth-palps, of an adult oyster he 

 will observe in the first place the quite marked difference in appear- 

 ance of the two, the first showing very plainly, in their ribbed or 

 striated surfaces, the series of closely approximated tubes of which 

 they are made up; the other looking as if quite firm and solid. In 

 the second place it will be noticed that the four palps, which look 

 like four triangular ears, being broader and rather pointed at or near 

 their centers, are so arranged, two within and two without, as to 

 form a U-shaped groove, with the mouth orifice of the animal occu- 

 pying the center o/ the arch of the groove, and each end receiving, 

 as one trough receives another when laid one within the other, the 



