BT N. A. COBB. 767 



of the four submedian lines. The cuticula is not striated. Lateral 

 organs in the form of slits occur close behind the cephalic setae. 

 When the head is viewed dorso-ventrally, these openings, which are 

 ordinarily invisible or at most barely glimpsed as transverse lines 

 one-fourth as long as the head is wide, come clearly into view as 

 two narrow passages leading inward and backward. A unicellular 

 ventral gland is present in all the species. Near the nerve-ring, 

 which encircles the oesophagus squarely and is about as wide as 

 the oesophagus at the point encii-cled, lie six longitudinal masses 

 of nerve-cells, of which the four larger are submedian and the 

 two smaller median. All the known species are eyeless. The 

 pharynx is a mere shallow conoid depression surrounded by three 

 rudimentary lips, which rarely bear papillae. The oesophagus is 

 conoid and terminates in an obscure cardia, which barely penetrates 

 the thin-walled intestine. The cardiac collum is shallow but 

 distinct. The rectum is equal in length to the anal diameter. 

 The tail is conoid in its anterior part, while the remainder — more 

 than half — is slender and narrowly conoid to the slightly swollen 

 ellipsoidal terminus, which bears a conical outlet for the caudal 

 glands. The lateral fields are usually inconspicuous. The reflexed 

 portions of the two symmetrically -placed ovaries, contrary to the 

 general rule, are nearly cylindrical. Both before and behind 

 the vulva occur unicellular glands. The eggs do not begin segmen- 

 tation until after being deposited. The male possesses no bursa 

 and none but inconspicuous papillae. Certain anal hairs, so small 

 that they are readily overlooked, probably serve as male papillae. 

 A sigmoid, tubular and chitinous accessory organ occurs in the 

 ventral region just in front of the two equal spicula. The anterior 

 straight testicle, directed forward, is invariably somewhat larger 

 than the posterior one, which is also directed forward and presents 

 the peculiarity in most of the species of being reflexed near its 

 free extremity. Of the two testicles, the anterior is connected 

 with the vas deferens by the longer duct. The ductus ejaculatorins 

 is narrow and composed of two rows of cells. The numerous 

 spermatozoa are more or less elongated and each possesses an 

 elongated nucleus. The species live among algae, and are probably 



