HYMENOLEPIDID^: 323 



as Sonsino, it also lives in the flea of the dog (Ctenocephalus canis) 

 and in the flea of man (Pulex irritans), but not in its larva. The 

 adult segments, which also leave the rectum of dogs and cats 

 spontaneously, creep about around the anus and get into the hair, 

 and are thus partly dried and disintegrated. Part of the segments, or 

 the oncospheres released by disintegration, are then taken up by lice 

 and fleas, within which they develop into larvae (cysticercoids). Dogs 

 and cats are thus infected by their own skin parasites, which they bite 

 and swallow whilst gnawing at their fur. The infection of human 

 beings must occur in an analogous manner, by transmission of the 

 cysticercoids present on the lips or tongue of dogs when the latter lick 

 them, or it may be that the vermin of cats and dogs harbouring cysti- 

 cercoids are accidentally and directly swallowed by human beings. 



Family. Hymenolepididse, Railliet and Henry, 1909. 

 Genus. Hymenolepis, 1 Weinland, 1858. 



Accessory sac (opening into genital atrium) usually absent. Vas deferens with 

 an external (outside cirrus sac) and an internal (inside cirrus sac) "seminal vesicle." 

 Three testes in each proglottis. The eggs are round or oval with two to four distinct 

 envelopes. In mammals and birds. 



Hymenolepis nana, v. Sieb., 1852. 



Syn. : Ttenta nana, v. Sieb., 1852, nee van Beneden, 1867; Tania agyptiaca, 

 Bil., 1852 ; Diplacanthus-nanus, Weinld., 1858 ; Tcenia (Hymenolepis] nana, Lkt., 

 1863. 



The worm is 10 to 45 mm. in length and o'5 to 07 mm. in breadth ; 

 the head is globular, 0*25 to 0-30 mm. in diameter. The rostellum 

 has a single circlet consisting of twenty-four or twenty-eight to thirty 

 hooks, which are only 14 //, to 18 p in length. The neck is moderately 

 long; the proglottids are very narrow, up to 200 in number, 

 0*4 to 0*9 mm. in breadth, and 0*014 t 0*030 mm. in length. The 

 eggs are globular or oval, 30 p to 37 //, to 48 //, ; the oncospheres measure 

 16 fj, to 19 fj, in diameter, with two coats, separated by an intervening 

 semi-fluid substance (fig. 224). 



This species was discovered by Bilharz in Cairo in 1851 ; it was 

 found by him in great numbers in the intestine of a boy who had 



1 The genus is by some authors divided into two sub-genera Hymenolepis, s. str., and 

 Drepanidotaenia, Raill. 



Drgpamd>tenia.Body t broad lanceolate, testes three, female genitalia antiporal beside 

 the testes. Scolex small, with eight hooks. Neck very short, longitudinal muscle bundles 

 very numerous. No accessory sac opening into genital atrium. 



Hymenolepis. Narrow, female genitalia ventral to or between testes. 



