BY N. A. COBB. 



459 



especially at the base of the pharynx. This last is two-thirds as 

 wide as deep, and. bears a small dorsal tooth behind the middle, 

 and two large sub-equal or equal submedian teeth, each of which 

 extends about three-fourths the distance to the lips and there 

 ends (opposite the bases of the cephalic setse) in a sharp perforated 

 point. Anteriorly the oesophagus is one-third as wide as the 

 neck, excepting, of course, where it swells to receive the base of 

 the pharynx ; posteriorly it becomes one-half as wide as the neck. 

 The cardiac collum is distinct but not conspicuous, and the cardia 

 itself large. There is no very distinct cardiac cavity. The intes- 

 tine is one-half as wide as the body. Though it often contains 

 diatoms, I do not think the species exclusively diatomivorous. 

 The narrow duct of the ventral gland terminates in a small 

 ellipsoidal ampulla, which empties through the porus excretorius 

 half-way between the base of the pharynx and the nerve-ring. 

 The nerve-ring is nearly as wide as the oesophagus at the point 

 encircled, and is but a trifle oblique. Near it, both behind and 

 in front of it, I have often seen a few large and transparent cells, 

 from some of which one or more processes passing into the 

 adjacent tissue could be observed. Doubtless they were nerve- 

 cells. They occur in the dorsal and lateral regions, but I do not 

 mean by this statement to imply that they do not equally 

 occur in the ventral region. At least as many as eight such cells 

 may occur in the neighbourhood of the ring. 



Four distinct unicellular lateral organs lying between the 

 oesophagus and the body-wall occur near the nerve-ring, two 

 behind and two in front of it. These organs seem to me espe- 

 cially interesting, and I shall describe them somewhat minutely. 

 The two posterior of the four organs are removed from the nerve- 

 ring a distance about equal to their own length, but they are not 

 exactly opposite each other, the one on the right hand side being 

 nearer the ring than that on the left hand side. The two anterior 

 organs are even less symmetrically placed. The one nearest the 

 ring, the right, is about as far in front of the ring as the left 

 posterior one is behind it. The more remote anterior one, the 

 left, is twice as far from the ring as that just described. Thus it 



