INTESTINAL WORMS. 167 
worms appears to be similar, and for the purpose of secretion; a 
renal secretion, as VAN BENEDEN supposes*.] In the thorn-headed 
worms there are two lateral canals situated beneath the skin that 
run the whole length of the body. 
We have already remarked that special respiratory organs are 
wanting. So far as any action occurs between the air of the 
medium in which these animals live and their nutrient fluid, it must 
be effected by means of the skin. But Entozoa live, for the most 
part, in situations where the atmosphere exists in a condition very 
impure and unfit for respiration; or where no air at all can enter, 
as in the liver, brain, kidney, &c. It is therefore probable that 
they derive from the fluids absorbed from the animals in which they 
live, the quantity of oxygen necessary for their life, and that they 
experience the influence of this gas only mediately through the 
animals in which they live ?. 
With respect to propagation: no genital organs, as noticed 
above, have been detected in Cystic worms. What many writers 
have described as eggs in these worms are calcareous corpuscles 
beneath the skin, which also occur in Tape-worms. Their multi- 
plication is effected by gemmation. In Canwrus there arise on the 
bladder on which the worm, or that extremity of it that bears 
the head, is seated, little buds which again develop other buds; in 
Echinococcus new bladders are formed within the parent bladder, 
like cells within cells, in which young Echinococci are developed 
that continue hanging by a thread for a time, after the containing 
envelope is ruptured, and then fall into the cavity of the parent 
bladder*. In Cysticercus the mode of propagation is yet unknown. 
In Trematoda there is found.on the abdominal surface, generally 
nearer to the anterior than the posterior extremity, an opening 
common to the organs of both sexes. From this a penis, usually 
named Cirrus*, can be evolved; near this peat the vagina opens. 
1 VAN BENEDEN Lettre relative & UV Hist. des vers cestoides, Ann. des Sc. nat. 3e Série, 
Zool. Vol. XVII. pp. 21—30. 
2 Comp. on the respiration of intestinal worms, Rupotput /ist. nat. Entozoor. 1. 
pp. 239—244, and CLoqueT Anat. des vers intestins, pp. 42—44. 
3 MUELLER in the Jahresbericht for 1835, Archiv. s. cvIl. CvIlI.; V. SrEBOLD in 
Burpacu’s Physiol. 2te Auflage 11, s. 183—185. 
4 See the fig. of Distoma hepaticum in MEHLIS, figs. 8, 9, 11. In fig. 8 is seen 
near the cirrus the opening of the vagina, through which a bristle has been passed to 
distinguish it. 
