37 



THE ANIMAL PARASITES OF MAN 



consisting of protractors and retractors, moves the spicules. The 

 protractors or exsertors in the large Ascaridae consist of four flat 

 band-like muscles which surround the spicule sac. Two long muscle 

 cells which arise proportionally far forward on the dorsal side of the 

 lateral line and are inserted into the base of the spicules serve as 



retractors. The spicules can be projected 

 o from the cloacal orifice (anus) during copu- 



lation, and when they are introduced into 

 the vagina they serve as prehensile organs, 

 perhaps also as stimulatory organs. 



FIG. 266. Male of the 

 rhabditic form of An- 

 giostonium nigrovenosuni. 

 A. t anus; /., mid-gut; 

 T., testicular tube; O., 

 oral orifice ; P., papillae ; 

 Sp., spicule. Magnified. 



FIG. 267. Transverse section through the 

 posterior extremity of the body of Ascaris 

 lumbricoides (male). The intestine is in the 

 middle, and the lateral lines are subjoined 

 thereto ; above the intestine the two spicule 

 sacs are seen ; below is the ductus ejaculatorius. 

 The muscular fibres are between the lateral 

 and median lines. Magnified. 



BURSA COPULATRIX. The males in many genera possess epidermal 

 wing-like appendages at their posterior extremity. These are supported 

 by elongated tactile papillae called ribs. In the most highly developed 

 bursae, e.g., in the Strongylidce, the ribs are called rays, as they consist 

 not only of nerve fibres but mainly of " pulp/' i.e., prolongations of 

 the subcuticular layer. Bursae are either open, i.e., bilaterally 

 symmetrical, or closed, when the posterior border is continuous all 

 round. A pseudo-bursa is one unsupported by ribs or rays, e.g., in 

 Trichuris. The bursa serves as an organ of prehension during 

 copulation. Some forms, moreover, carry a sucker at the posterior 

 extremity (e.g., Heterakis) ; in others the spicules and other pre- 

 hensile organs are absent ; they are then replaced by an evertible 

 cloaca, e.g., Trichinella. 



