EXAMINATION OF CYSTICEECOID STAGES 159 



as a rule, to the genera Hymenolepis and Davainea. The Hymeno- 

 lepis varieties are characterized : by the position of the genital pore, 

 which is always at the left border of the segment ; by the triple 

 formation of the testes ; by the presence in the vas deferens of an 

 outer and inner vesicula seminalis ; by the sac-shaped uterus ; and 

 by the single row of hooks upon the rostellurn. The Davainece 

 possess a double row of hooks upon the rostellum, together with 

 several rings of booklets leading into the suckers ; the uterus, more- 

 over, disappears, leaving one or more eggs in so-called parenchyma- 

 capsules. H. lanceolata (Bloch) of ducks and geese is an excellent 

 example of the genus Hymenolepis. 



(3) NEMATODES (THREADWORMS). 



Living specimens of the larger' Nematodes, such as A scar is meg alo- 

 cepliala of horses, A. suum of swine, and A. lumbricoides of man, are 

 readily obtainable. They should be examined in the first instance 

 with the naked eye. 



The distinctive sexual 

 characteristics will be appar- 

 ent if adult specimens of both 

 sexes are examined side by 

 side. In both, the body is long 

 and spindle - shaped and 

 pointed at the posterior end. 

 The male, however, is smaller 

 and slighter than the female, 

 and has the posterior end of FlG . 8L _ As caris lumbricoides, L. Male. 



the body recurved towards the A -> Posterior extremity. B., Anterior ex- 



-, e mi tremity, dorsal aspect. C., Anterior extremity, 



ventral surface. The male ven tral aspect. P., Excretory opening. gf ft 



differs also in having no special Spicuia. (After ciaus.) 

 genital opening ; the genital 



organs, which are termed " spicules " and which appear as two small, 

 yellowish-brown rods, issue from the anus, which is placed close to the 

 hinder end of the ventral surface of the body (fig. 81). In the female, 

 the genital opening is also upon the ventral surface, situated at the 

 border-line of the anterior and middle portions of the body and some 

 considerable distance, therefore, from the anus. It will be seen with 

 the naked eye if the body-surface, which is here slightly indented, is 

 dabbed with filter-paper. The papillae which surround the anal 

 opening of the male will be seen only with a strong glass. The 

 mouth-opening is terminal in both sexes and is surrounded by three 

 papillse or lips, one placed dorsally, two ventrally. Immediately 

 behind the mouth papillae, in the median line of the ventral surface, 



