38 ON PARASITES. 



THE STROBILA 



matures posteriorly, and as the joints separate they are called pro- 

 glottides. They contain in their interior eggs for a new generation. 



The question has been raised whether a proglottis ought to be 

 called an individual or not. 



Each proglottis possesses distinct male and female organs, — fecun- 

 dates itself — possesses the power of independent motion . It possesses 

 the characteristics of an individual and may be called one. 



The formation of joints by this process of budding may go on in- 

 definitely, special circumstances only putting an end to the act- 

 The number of eggs set free from them in the outer world is pro- 

 digious, each strobila furnishing many millions. But for the special- 

 ized conditions necessary for the development of these worms, they 

 would starve the larger animals by robbing them of their food. A 

 suf&cient number of species of cystic and cestoid worms have been 

 found to pass through the preceding metamorphoses, to afford a suf- 

 ficient proof of the generality of the laws which regulate the develop- 

 ment of entozoa. 



The liver of the mouse, when affected with Cysticercus fasciolaris, 

 if fed to cats will infest those animals with the Taenia crassicollis. 



The Cysticercus pisiformis of hares and rabbits is converted into 

 the Taenia crassiceps of the fox. The Cysticercus tenuicoUis becomes 

 the Taenia serrata and the Cysticercus cellulosae, the Taenia solium. 

 From the Caenurus cerebralis, comes the Taenia caenurus, and from the 

 Echinoccus veterinorum a Taenia echinocci. 



The chief dil£culty is prosecuting investigations upon those ento- 

 zoa, is to obtain the right animals to experiment upon. But with 

 that skill, which only comes from experience, i. e. observations of a 

 large number of similar facts, it is to be expected that increased 

 facility in artificially propagating these creatures will be acquired. 



With adequate knowledge of the history and habits of the entozoa 

 will come an improved method of prophylaxis against them, and skill 

 in their treatment, both of which are yet quite rudimentary. 



The Nematoidea still remain in great uncertainty, with regard to 

 their embryology. 



The formation of the ovule and zoosperm, and the fecundation of 

 the former by the latter have been observed with much care by 

 Nelson, Meissner, Thomson, Leuckart and others ; but the subse- 



