136 



ROUNDWORMS. PHYLUM NEMATODA 



of the red pigment haemoglobin (p. 190), with a high affinity for 

 oxvgen which is presumably used in respiration. Haemoglobins 

 are also present in other parts of the worm. The nuclei of the 

 ectoderm, except at the hinder end, are collected along the mid- 



cLn- dJ- 



Int- 



ex.c. 



-vc-L. 



\:rv 



Fig. 99. — A transverse section through the middle of the body of a female 



Ascaris lumbricoides. 



cu.. Cuticle ; d.l., dorsal line ; d.n., dorsal nerve ; ect., ectoderm ; egg ; eni., endoderm ; ex.c, excretory 

 ' canal; int., intestine: /./.. lateral line; m.f., muscle fibre; ov., ovary; p.c, perivisceral cavity; 

 ut., uterus ; v.L, ventral line ; r.n., ventral nerve. 



dorsal, mid-ventral, and lateral lines. Along these lines the 

 protoplasm bulges towards the body cavity. A nerve cord is 

 embedded in the dorsal and ventral lines, and a canal in each 

 lateral line. The canals have no internal openings ; they unite 

 in front to open by the excretory pore ; in the free-living Rhabditis 

 they have been shown to expel a fluid to the exterior. The two 

 have but one nucleus, which is very large, and lies in the wall of the 

 left-hand canal, near its front end. Thus they may be said to be 

 hollowed in the body of one immense cell. Two more nuclei lie in 

 the wall of the median duct to the exterior. Four very large, 

 hr^nrhofi cells lie upon the lateral lines near the anterior end of the 



