THE MICROSCOPE. 



end- of one pair of gill-leaves, the grooves of the gill-leaves thus 

 passing into and coinciding with the grooves or groove of the labial 

 palps, and the strings of food from the gill-grooves, one upon either 

 side, would thus meet and disappear down the mouth orifice. 



A more careful examination will show that the outer palps are 

 continuous around the outer side of the groove of the U from the 

 outside of the gill-leaves of one side to the outside of the gill-leaves 

 of the other, although just above the mouth orifice there is a depres- 

 sion or cutting out of the border to about one half or even more of 

 the depth of the palps, making two ears or lobes, one upon either 

 side and connected around the mouth by a portion of the border, 

 which is only one half or less as broad as it is elsewhere. The inner 

 palps are in like manner continuous from the inside of the two gill- 

 leaves of the other and are in like manner somewhat separated by a 

 depression in the region of the mouth, although this depression is 

 not as deep as in the outer border. As has already been stated, the 

 proboscis when gathering food from the gills is arched forward and 

 the lip encloses, or surrounds, the cephalic ends, and accordingly 

 the ends of the grooves of the four gills, the slit of the lip being on 

 the side away from the gills. Now, as the body in its growth 

 encroaches upon the length of the proboscis, the proboscis becomes 

 necessarily somewhat straightened and shortened, and at the same 

 time the lip becomes somewhat elongated upon the side toward the 

 gills, in order to still connect, as a single trough, the gills and the 

 mouth ; in fact the lip becomes nearly if not quite as long as the 

 proboscis itself. With this change in the shape of the lip there 

 occurs also a change in its surface, brought about by the formation 

 across the lip from side to side on that portion away from the mouth 

 orifice, or between it and the gills, of a series of ridges which ulti- 

 mately grow up in such a manner as to form a fringe of tentacles 

 extending from the inner side of the gill-leaves of one side around 

 by the mouth orifice in a U shape to the inner side of the gill-plates 

 of the other side, thus forming the rudiments of the inner palps 

 inside of and parallel to the edge of the lip which is turned up and 

 represents the rudiments of the outer palps. By the formation of 

 these tentacles a groove is formed between the fringe and the edge 

 of the lip which becomes the U-shaped food groove already men- 

 tioned. The general structure of the palps seems to indicate that 

 very soon after this groove has been formed by the growth and 



