T^NIA ECHINOCOCCUS 



345 



is spirally coiled; the cirrus pouch is pyriform. The ovary is horse- 

 shoe-shaped with the concavity directed backwards; the vitellarium 

 double, each half almost bean-shaped, at 

 right angles to the plane of the segment ; &jb 

 the shell gland is round. The median trunk \. \ 

 of the uterus is dilated when filled with eggs 

 and (instead of lateral branches) has lateral 

 diverticula. It is not unusual for the eggs 

 to form local heaps. The embryonal shell 

 (embryophore) is moderately thin, with radial 

 striae, almost globular, 30 /ju to 36 /JL in 

 diameter. 



When mature this parasite lives in the 

 small intestine of the domestic dog, the 

 jackal, and the wolf, and apparently also in 

 Fells concolor, and is usually present in great 

 numbers ; it can also be transmitted ex- 

 perimentally to the domestic cat, one suc- 

 cessful result out of seven (Deve). 1 The 

 larval stage (Echinococcus polymorphic) lives 

 in various organs chiefly in the liver and 

 lungs of numerous species of mammals 

 (twenty-seven), especially in sheep, ox and 

 pig, and it is even not uncommon in man, 

 though the Tasnia itself has never been found 

 in a human being; accordinglyman can only 

 acquire the echinococcus by ingesting the 

 eggs of the " dog worm." The dogs dis- 

 seminate the eggs of Tcenia echinococcus 

 wherever they go, or carry them to their 

 mouths and coats by biting up the 

 evacuated segments, and are thus able to 

 transmit them directly to human beings (by 

 licking them or making use of the same 

 crockery, etc.). In other cases the onco- 

 spheres, enclosed in the embryophores, must ?' the sid f s ^recognizable in 



J * the second proglottis ; the pos- 



withstand desiccation for a time and then terior proglottis shows the uterus 

 (as when the dogs are "kissed" or other- Ttt d^s S^fh'e ^na" 

 wise caressed) are transmitted into or on to 50/1. 



1 In Iceland 28 per cent, of the dogs are infected with this Tsenia, in Lyons 7'i per cent., 

 in Zurich 3^9 per cent., in Berlin I per cent., and in Copenhagen 0-4 per cent. In Australia 

 even 40 to 50 per cent, of the dogs are affected. It is, however, a question whether, in addi- 

 tion to T(znia echinococcus , a second analogous form is not involved, as the form from Cants 

 dingo attains a length of 10 to 30 mm. 



FIG. 250. Tcenia echino- 

 coccus : the cirrus sac, the 

 vagina, uterus, ovary, shell gland 

 and vitellarium, and the testicles 



