424 Prof. C. Claus on the Morphology and 



simplification of the organization, the anterior section of the 

 body armed with its suckers and chitinous hooks, which was 

 at an early period invaginated into the posterior portion and 

 surrounded by this as by a protecting envelope. The evident 

 necessity for protection, which was to a certain extent satis- 

 fied by this process, may also have determined the change of 

 function of the tail, which from an organ for effecting the 

 change of locality was transformed into a larger or smaller 

 vesicle, accommodating the whole of the scolex inside itself ; 

 or again — and in all those cases in which the simple invagi- 

 nation of the scolex-head into the scolex-body gave a sufficient 

 protection — degenerated into an apparently functionless rudi- 

 ment, in order in the end to drop off entirely (Bothriocephalus). 

 In the first case, however, in which the tail became a large 

 vesicle filled with watery fluid, its great increase in size 

 enabled it to acquire yet another important function — prolife- 

 ration — and to produce by budding numerous scolices 

 (C&nurus), in some cases brood-capsules with scolices, either 

 directly or by means of a second and third generation of 

 vesicles (Ecliinococcus) . While the metamorphosis was 

 simplified in one direction, in the case of degeneration and 

 shedding of the caudal appendage, into a more direct deve- 

 lopment, in the other it grew more complicated and assumed 

 various forms of alternation of generations. In the latter, to 

 a certain extent by way of compensation for diminished 

 productiveness, owing to the loss of pasdogenesis, the neces- 

 sity for increasing the race was satisfied in a newly acquired 

 way, namely by means of budding on the enlarged surface of 

 the vesicle. 



The power of proliferation, which has been only second- 

 arily acquired by certain Cysticerci (Ccenurt and Echinococci) } 

 was, like the process of proglottid-forming by the strobila, 

 wrongly used as a standpoint from which to interpret the 

 whole Cestode development. From this point of view the 

 scolex was regarded as the gemmation-product of the embryo, 

 the proglottis as that of the scolex, and, in accordance with 

 the interpretation of the individualized joints of the Cestode 

 as sexual animals, the complicated five-jointed scheme of the 

 Cestode-metagenesis was set up. In this arrangement the 

 embryo figured as primary nurse-form, the scolex as nurse, 

 and the proglottis as sexual individual, while the Cysticercus- 

 and Strobila-stages, which furnish the connexion between 

 primary nurse- form and nurse, and between nurse and sexual 

 individual, were regarded as polymorphic colonies. 



Thus then the metamorphosis of the parasitic Platyhel- 

 minthes led in the case of the Trematodes, owing to the psedo- 



