FREE-LIVING NEMATODES 471 



proved. The apparent connection in the parasitic species between 

 the excretory organ and the lateral fields is incidental, the action 

 of the body muscles tending to locate such long slender tubular 

 organs in the region of least motion, namely the lateral region. 

 In these parasitic species the organ is often bifurcated a little be- 

 hind the excretory pore (apparently on account of the increased 

 size of the whole organism), and thence backward the tubular 

 elements are attached to or lie in or near the lateral fields. This 

 suggests that the mystery surrounding the excretory organ in 

 some of the free-living species may perhaps be solved by search 

 directed toward the discovery of a bilaterally symmetrical renette. 

 Dorylaimus, a genus containing some of the largest free-living 

 nematodes, is a case in point. The renette ceU often has smaller 

 companion cells in its immediate rear. 



The caudal glands, so common in the tail end of the free-living 

 nematodes, serve to cement the tail end to any convenient object. 

 In thus attaching themselves nematodes sometimes show great skill 

 and pertinacity. The terminus of the tail bears a minute spiimeret 

 through which the secretion of the glands is forced out, and by means 

 of which its flow may be regulated, much as in the case of spiders. 

 The secretion is a cementing substance insoluble in water. The 

 caudal glands are normally three in number and are usually located 

 single file in the anterior part of the tail, or somewhat farther forward 

 in front of the anus. Two of the ducts often unite to form one duct; 

 sometimes all three unite. Just in front of the pore in the spin- 

 neret the ducts may enlarge to form one or more ampullae. Caudal 

 glands are absent in most of those species in which the males are 

 supplied with lateral caudal flaps constituting the bursa. It is 

 possible that the secretion of the bursal ribs, or tubes, is of the 

 same general character as that of the three caudal glands, and that 

 these two sets of glands are homologous. The ribs of the bursa, 

 when the full complement is present, consist of three groups. This 

 is at least suggestive. The females of such species sometimes have 

 lateral pores on or near the tail. 



The sexual organs originate from a few cells set off for the pur- 

 pose early in the development, which for a time remain rather 

 quiescent near the center of the body. As the nematode ap- 



