208 ANIMAL PARASITES AND MESSMATES. 



been found in the Delphinus delpliis, the Titrsio, and the 

 Ziphius. As the Orca attacks the whale, and feeds 

 upon its flesh, there would be nothing surprising in our 

 finding in these large cetacea, some agamous cestode 

 destined to pass through the last phase of its evolution 

 in this terrible carnivorous animal. 



The cestode can scarcely be called a parasite under 

 the first vesicular form. It is sufficient for it to pass 

 through its first transformation in the midst of the 

 tissues, and it will remain weeks, months, even years, 

 without undergoing any change ; it asks for nothing but 

 an hospitable roof ; and this mysterious being, that had 

 often come they knew not whence, encamping rather than 

 lodging, always without progeny, was long since cited 

 by the naturalists of a former age in favour of the old 

 hypothesis of spontaneous generation. 



It is not the same with the second form. Here the 

 worm, always lodged in the intestines, grows with extra- 

 ordinary rapidity, and fulfils all the conditions of a true 

 parasite. In a fertile soil it extends itself and produces 

 young as long as it has any life, and in no group of the 

 animal kingdom do we find any fecundity to be compared 

 to that of this worm. Boerhaave described a broad tape- 

 worm, three hundred ells in length. Eschricht estimates 

 the number of the segments of this worm as ten thou- 

 sand ; and if we consider that each segment, or, we 

 should rather say, each complete worm, may perhaps 

 enclose thousands of eggs, we may form some idea 

 of the profusion of germs which can be scattered by 

 each individual. 



To thoroughly know an animal we must have made 

 observations on it during all the phases of its evolution. 



