ANIMAL PAEASITES. 39 



world with the excrements, which then appear as if sprinkled with 

 fine white sand; or immediately without the intestine, where, as 

 was even stated by Dujardin, the progress of the proglottis is 

 seen indicated by a white, milky streak. Sometimes the pro- 

 glottis does not burst in either of the above-mentioned places, but 

 gets uninjured into the intestine of a new host, in which case it 

 only distributes its brood after it has been destroyed by digestion. 

 According as the eggs reach the intestine of their host in this 

 way separately, or enclosed in the proglottis, and therefore in a 

 mass, solitary or numerous specimens of a cystic worm, or of 

 the analogous state, are produced within one and the same host. 

 With regard to the duration of the existence of the proglottides, 

 which are passed sometimes with, and sometimes without, fsecal 

 matter, we know nothing ; moist soils, upon which they creep about, 

 keep them alive longer than dry ground, and they live more than 

 eight days in carefully-renewed white of egg. The capability of 

 evolution of the enclosed brood is of longer duration than the 

 life of the proglottides, as the putridity and mouldiness of the 

 proglottides do not destroy this faculty in the brood. 



In consequence of their power of independent motion, they 

 quit the places in which they have been deposited with or with- 

 out excrementitious matter, creeping away from the dung upon 

 all sorts of moist objects in the meadows (such as stalks of grass, 

 clover, low plants, roots, salad, windfalls, &c), and upon the 

 foliage of trees, when they have been dropped upon the latter 

 with the excrements of birds. In this way they are devoured by 

 vertebrate and invertebrate animals which feed upon grass, 

 raw fruit, roots, leaves, &c. If they get into water they burst 

 and disseminate their brood in that fluid, where it may reach 

 the stomachs of other animals with their drink. In cess- 

 pools and drains the Tcenice of the human subject evacuate their 

 eggs, and are then thrown upon salad, grass, roots, &c, as 

 liquid manure, or swallowed by pigs which wallow in such filth. 

 In predaceous fishes which live upon their own species, the mature 

 Cestodea of the smaller specimens get into the stomachs of the 

 larger ones, when they disseminate their eggs, and thus infect 

 the latter with Cysticerci. On a dry soil their vitality may only 

 last for a few hours. 



The proglottides, therefore, in the first place, perform an active 

 migration from within the intestine of their previous host and are 

 thus passively transferred into the ivitestinal canal of a new host. 



