BOTHRIOCEPHALUS LATUS. 101 



into mature Bothriocephali in the intestines of higher fishes, or 

 of the marine hirds of prey which live upon these fishes. Whether 

 these creatures in the intestine of the fish have been developed 

 there, or whether they only reached the intestine with one of 

 the animals on which the fish feeds (as, for instance, a crab, 

 a mollusc, or an insect), in which they had become converted 

 into a scolex, after the animal had swallowed the eggs of the 

 mature Bothriocephalus to which they belong, is still unde- 

 cided. There may, therefore, be two possible ways for the pro- 

 duction of the mature Bothriocephali. Either the lower animal, 

 which harbours the scolex in the same way that the host of the 

 Cysticercus bears those creatures, is devoured by an animal 

 (such as a large predaceous fish, bird, or mammal), in the 

 intestine of which the scolex, being set free, immediately 

 developes itself; or the first-mentioned animal is first of all 

 swallowed by another, in the intestine of which it certainly passes 

 through the same preliminary changes which occur when a 

 Cysticercus gets into a suitable alimentary canal, but is unable 

 to develope these to maturity. It is only when this second 

 animal is devoured by another belonging to a higher species, that 

 the scolex attains the conditions by which it can become deve- 

 loped into a mature Bothriocephalus. At present, certainly we 

 cannot say whether in particular species of Bothriocephali only 

 one or the other of the above-mentioned direct or indirect 

 processes takes place, or whether both paths are followed by one 

 and the same species, as if nature wished to secure to each 

 individual the broadest possible base of probability for the 

 preservation of its species. It is true that, in the latter case, 

 we must suppose that the host of the mature Bothriocephalus 

 can obtain the first animal which harbours the scolex outside its 

 intestine, as well as the second, which contains it within the 

 alimentary canal, and use them both as food. 1 Here, unfor- 



1 Von Siebold, as I have already mentioned, was the first to produce artificially in 

 Teenies a grade of development, which, in its nature corresponds with the scolices 

 belonging to the Bothriocephali. Thus, if rabbits be fed with Cysticerci of the rabbit, 

 or dogs and cats with Cysticerci which do not find a favorable soil for their perfect 

 development in the intestines of those animals, but gradually become abortive therein, a 

 form is obtained which bears, instead of an articulated Cestode body, a simple, inarticu- 

 lated, hand-like, flat, massive appendage, not furnished with a caudal vesicle. Such 

 animals attain a length of 10 to 20 niillim., and are the perfect analogues of those 

 scolex structures which are met with in the intestine of the sticklebacks and other 



