THE MICROSCOPE. 



modification of the ridges, the central part of that portion of the lip 

 which lies between the ends of the gills and the body is folded up 

 and pushed between the two sets of gill-plates, the edge finally being 

 brought back to near the mouth orifice ; or absorption of the tissue 

 taking place along the middle of the lip so as to divide the lip into 

 two halves, thus leaving a doubling of the edge of the lip around 

 the end of each set of gill-plates and the lip as thus bent and 

 divided would exactly outline the food-groove and the labial palps 

 as we find them in the adult. In this case the ridges, which I have 

 stated as forming from the surface of the lip, would form a ribbed 

 lining or inner surface to each palp, as this appears to be actually 

 the condition of affairs. If the lip, however, does not fold up 

 between the U-shaped fringe of tentacles, then the inner palps 

 would agree in their theory of formation with the gills, except that 

 the tentacles originate from the lip instead of from the body proper 

 and do not fold up, and the outer palps would be composed of the 

 outer edges of the lip, with a lining of ridged or tentacular origin. 

 In regard to this point, however, I have no material at the present 

 time to assist me in deciding ; hence, I cannot say whether the lip 

 proper does or does not, by folding between the gill-leaves and 

 toward the mouth orifice, take any part in the formation of the inner 

 palps, other than to form a base from which the palps arise. This 

 base or lower portion of the lip finally becomes attached permanently 

 to the body and the ends of the gills by the intergrowth of connected 

 tissue and the adult form is attained. It may be as well to state 

 that, notwithstanding the different sources of origin of the gills and 

 labial palps, they are both undoubtedly outgrowths from the exoderm. 

 It will thus readily be seen that the proboscis is of considerable 

 importance in the life of an oyster, acting as it does in the double 

 capacity of, first, an accessory food gatherer, and, second, as the 

 framework for the palps which direct and guide to the mouth orifice 

 the strings of food-particles which have been arrested by the gills 

 and rolled down to the grooves and onward to the mouth by the 

 •action of those vigorous and almost constant workers, the gill-cilia 



