438 Miscellaneous. 



Tcenia and Bothriocephalus will throw some light on this point. The 

 latter worm only occurs in SA?vitzerland, Poland and Holland, whilst 

 the Tcenia inhabits the intestines of the French and Germans. When 

 individuals belonging to these two nations live for a certain time in 

 Switzerland, they sometimes get the Bothriocephalus^ but never the 

 TtEuia. In all the countries in which the Bothriocephalus is so fre- 

 quent, it is customary to water the plants used as food with the liquid 

 excrement procured from the cesspools. There is no doubt that some of 

 the eggs of the Bothriocephalus ejected with the excrements find their 

 way, with salads and other raw vegetables, into the human intestines. 

 These eggs contain a little embryo, which exhibits very lively move- 

 ments of contraction and dilatation ; the anterior portion of its body 

 is furnished with six retractile hooks. In the pulmonary cavity of 

 the common slug, some little, milk-white cysts of y^ inch in dia- 

 meter frequently occur ; each of these contains a young Tcenia. It 

 is very probable that as soon as the slug has been devoured by some 

 other animal, the worm quits its envelope and developes new seg- 

 ments. The animals of the genera Scolex and Tetrarhynchus, which 

 are so often met with in the intestines of marine fishes, are only the 

 young cephalic segments of Tcenice, which afterwards fix themselves, 

 after losing the trunks armed with hooks, which are useful to them 

 during their migrations in the bodies of fishes. 



Occasionally the Tcenia loses itself during its peregrinations ; its 

 metamorphoses then become arrested, and certain portions of its body 

 undergo morbid transformations ; hydatids are nothing but abortive 

 TceniaSf of which the normal development sometimes depends upon 

 mere chance. The liver of rats and mice often contains an elongated 

 worm, the last segment of which is transformed into a bladder filled 

 with water ; but as soon as this passes into the intestines of a cat, 

 the terminal vesicle of the parasite disappears, it developes new seg- 

 ments, and becomes a true Tcenia^ long since described by naturalists. 



If during the summer some Lymncece or Paludince, of which the 

 shells have been removed, be held in pure water and their skins slightly 

 tora, numbers of microscopic worms will be seen to issue from them, 

 appearing in the water like whitish clouds. These creatures, whose 

 body is terminated by a tail, have often been classed amongst the 

 Infusoria under the name of Cercaria. The Monostomum mutahiley 

 which inhabits the aeriferous cells of aquatic birds, produces embryos 

 which swim quickly, and within which a second embryo may be seen 

 moving ; the latter completely resembles the worms which are found 

 in the hymncece, in which the Cercarice are formed. The primitive 

 embryos of the Monostomum probably leave the aeriferous vessels of 

 the birds when the latter are in the water, and afterwards penetrate 

 into the mollusks. Here the Cercarice are formed by genmiation, 

 and they have been seen to penetrate into the larvae of aquatic insects 

 by the aid of the corneous points which they bear on their heads. 

 During this passage they lose their caudal appendage, and then ex- 

 hibit the form of the Trematode worms. After this they become 

 contracted, and surround themselves with an envelope as transparent 

 as glass, within which they await their further development, which 

 only takes place according as the insects undergo their metamor- 



