i68 



NEMATHELMINTHES 



CHAP. 



is also a median dorsal canal which contains a few eggs. By 

 this time the wall between the ovary and the egg-sac has again 

 appeared. 



One of the most interesting points about the female is that, 

 according to Vejdovsky, the ovary is segmented, the cells which 

 form the ova being heaped up in segmentally-arranged masses. 

 This observation, if correct, is almost the only instance of seg- 

 mentation recorded in the group Nemathelminthes. 



The only other genus which is associated with Gordius in 

 the group Nematomorpha is Nectonema, of which there is as yet 



Fig. 87. Nectonema agile 

 Verrill. A, The adult. 

 Magnified. (After 



Fewkes.) B, Longitudinal 

 section through the head, 

 x about 20. (From 

 Burger.) a, Mouth ; b, 

 circumoesophageal com- 

 missure (dorsal) ; c, cell 

 of salivary gland ; d, 

 septum cutting off head 

 from rest of body ; e, 

 testis ; /, ventral cord ; 

 g, oesophageal cells ; h, 

 lumen of oesophagus ; i, 

 cerebral ganglion (ven- 

 tral). 



but one species known, Nectonema agile Verr. 1 Our knowledge of 

 the anatomy of this worm is due mainly to Burger 2 and Ward. 3 

 Nectonema is a marine worm found swimming near the surface of 

 the sea with rapid undulatory motion. The males are from 50 

 to 200 mm. long, the females from 30 to 60 mm. The body is 

 faintly ringed, and bears two rows of fine bristles on each side. 

 Owing to a curious torsion of the body through a right angle, 

 the lateral bristles of the anterior third seem to be placed in the 

 ventral and dorsal middle line. They are very easily broken off. 

 The body is divided into a small anterior and a large posterior 



1 A. E. Verrill, P. I. S. Mus. vol. ii. 1879, p. 165. 



2 O. Burger, Zool. Jahrb. Anat. Bd. iv. 1891, p. 631. 



3 H. B. Ward, Bull. Mus. Harvard, vol. xxiii. 1892-93, p. 135. 



