THE MICROSCOPE. 



a rather short intestine, and a pharynx or oesophagus which may be 

 protruded from the body as a sort of papilla with the mouth orifice 

 at its center, or contracted so as to form a roundish cavity inside 

 of the body walls. Gills are entirely lacking until about the time 

 the young animal becomes attached to some " rock," when they 

 begin to form as tubes, growing out from the body in two or four 

 rows, which finally double upon themselves and grow back towards 

 their origin in the body. The tubes of each row become united 

 with each other at their ends, and afterwards at other points 

 throughout their length, so as in a short time to form four double- 

 walled tube-leaves, two upon either side of what may be considered 

 for the present, the median dorsal line of the body, and extending 

 from near one opening of the alimentary canal to near the other. 

 Meanwhile the protrusite oesophagus grows out into a slender and 

 quite flexible proboscis, which is only slightly if at all extensible, 

 and is provided at its extremity with a spreading and very mobile 

 lip or rim which surrounds the mouth orifice and which is split 

 through upon the cephalic side, and the entire digestive tract has 

 becopie very much elongated and somewhat bent upon itself so as 

 to outline in some degree the folding of the tract as seen in the 

 adult. I first noticed this proboscis stage of growth of the young 

 oyster in the fall of 1878 when at work over the oyster beds in the 

 vicinity of Crisfield, Md. I had been opening some small speci- 

 mens of oysters, which were from J th to ^s^th of an inch in dia- 

 meter, for the purpose of studying their structure, when my atten- 

 tion was attracted by a backward and forward movement in the 

 water of something attached to one of the little animals, and which 

 I took at first to be a bit of the mouth or gill-plate, torn in taking 

 off the shell, but in pushing this waving bit of tissue to one side 

 with the end of a pencil, it spread out at the end and closed about 

 the point of the pencil, clasping it quite firmly, and upon closer 

 inspection I found that the bit of tissue represented the end of the 

 alimentary canal, and that the portion clasping the point of the 

 pencil was in reality a lip-like flap surrounding the mouth orifice of 

 the canal. The proboscis was endowed with a certain responsive 

 action since, whenever the point of the pencil was brought in con- 

 tact with it, the proboscis would move about and the lip be directed 

 towards the point of contact, when the pencil would be clasped as 

 in the first instance. If left to itself the proboscis would move 



