652 



HEM A THELMINTHUS 



which occupies the whole length of the body when filled with 

 embryos, evacuates its contents by a rupture close to the mouth 

 and just external to the papillae. The tail is rounded off, and 

 carries a small bent chitinous hook. 



Leiper states that the male is only 22 millimetres in length, and 

 has five pairs of papillae. 



Life-History. — The males and females live in the connective 

 tissue about the mesentery, and after copulation probably the males 

 die off. When the female is gravid, she moves, head first, appar- 

 ently in search of water, usually downwards towards the leg or 

 foot; more rarely she moves to the hand or arm, and very rarely 

 to the head. Arrived under the epidermis, she bores her way 

 through the deep layers, while a little bulla on the surface marks 

 her presence. 



When this bulla bursts, a small hole is seen, at the bottom of 

 which lies the vulva, through which the tube of the uterus has 

 prolapsed, bending the head to one side. Clear fluid can be seen 

 escaping from this tube, which, when examined, is found to be full 

 of embryos. 



Fig. 280. — Larva of Dracunculus medinensis Linn^us. 

 (After Looss, from Mense's ' Tropenkrankheiten.') 



The segmentation of the egg takes place in the uterus, and the 

 embryos are born alive. They are flat, pointed little bodies. 

 0-6 millimetre in length and 17-5 pi in breadth, with a narrow, very 

 pointed tail. The mouth is at the anterior end, and leads into an 

 alimentary canal with an anus. There is a little sac on each side 

 of the root of the tail. According to Leiper, these little larvae cannot 

 swim, but either die or are swallowed by a Cyclops. In this crusta- 

 cean they pass from the stomach into the aislom, where they develop 

 for four weeks. Leiper describes the lirst ecdysis as taking place 

 about the seventh to ninth day, and the second between the tenth 

 and eleventh day, after which progressive histological changes occur. 

 After the fourth week no further change takes place, though they 

 can live for forty-one days in the Cyclops. When placed in 0-22 per 

 cent, solution of hydrochloric acid, the Cyclops is promptly killed, 

 while the larva appears to be stimulated, undergoing ecdysis, and 

 escaping from the Cyclops by boring its way through the chitinous 

 cuticle. In a monkey fed with infected Cyclops, three females and 

 two males were found. It is, therefore, correct to assume that man 

 is infected by ingesting infected Cyclops with his drinking-water, 

 and it is probable that, set free in the stomach, the larvae enter the 

 connective tissue by boring their way through the stomach-wall. 



Pathogenicitv.-- The worm causes dracontiasis (see Chapter 

 LXXXVIIL). 



