6 The Microscope. 



shown in Plate I, figure 5, and Plate II, figure 17. It is probably 

 caused by the ends of the cilia approximated as in Plate II, figure 35. 

 The oral aperture proper is within and above these cdlia, a circular 

 orifice with somewhat protrusible lips, with which, assisted by the 

 suddenly expansive action of the cesophague, the food particles are 

 seized. 



Immediately behind the oral annulus o^e or more lines of 

 vibratile cilia extend across the ventral surface from the lateral 

 bands (Plate I, figure 5), This arrangement obtains in all the 

 species. On each side of the oral annulus in several forms there 

 is a tuft of adcurved cilia which merges into and is mingled with 

 the frontal tufts of tactile hairs on each side of the head. Their 

 function seems to be to assist in making a current that shall set in 

 toAvard the mouth and carry the food particles with it. Near the 

 four tactile tufts there are usually to be seen, on the ventral surface, 

 four small, hemispherical, refractive and colorless bodies that have 

 been called eyes. They are shown in Plate I, figure 5, from a 

 specimen exhibiting them with uncommon distinctness. I have not 

 been able to study them satisfactorily. 



The structure of the oral aperture is essentially similar in all 

 the species, and in all it opens directly into the CBSophagus, an organ 

 that varies in length and is extremely muscular. From the oral 

 orifice it extends more or less obliquely upward, then turns toward 

 the intestine, into which it enters for a short distance (Plate II, 

 figures 21 and 24). Near its middle it is usually constricted. Its 

 cavity is triangular, as shown in the transverse optic section, Plate 

 II, figure 18, and this peculiarity holds good in all the forms 

 observed by me. The contractions of the thick, muscular walls 

 enlarge this cavity and, assisted by the quick protrusion of the oral 

 aperture, draw in the food particles by what seems a suction force. 

 The motion is very sudden and snapping. The margins of the 

 triangular cavity are seldom straight and even, but irregularly 

 undulate or miniitely crenulate. The opening into the intestine is 

 circular. 



The tubiilar, tapering passage following the oesophagus serves 

 the purpose of both stomach and intestine. It takes nearly a straight 

 course in the median line of the body, being depressed from its 

 normal position by the egg. The walls are, as a rule, lined by a 

 single layer of nucleated cells. In Ch. lams, however, both Fernald 

 and Ludwig have seen an external, secondary layer of small, incon- 

 spicuous cells. In Ch. rhomboides I have doubtfully noticed a 

 similar arrangement. 



