The tape-worms are internal parasites of vertebrates. Their larvae (cysticerci or bladder-worms) are parasites of other vertebrates or of invertebrates. Dr. E. M. Walker has given me the following list of species that are found here. It is merely a beginning.
Dipylidium caninum (L.)—in the Dog and Cat (adult).
Taenia serrata Goeze—in the Rabbit (cysticercus).
saginata Goeze—in Man (adult).
" echinococcus v. Sieb.—in Man (cysticercus).
" serialis (Gerv.)—in the Rabbit (cysticercus).
Our only representative of this group that contains so very many marine species is the well-known Hydra, that has been the subject of such a large number of experiments in regeneration.
Hydra viridissima Pallas—(Dr. E. M. Walker). " polypus L—Sunnyside.
" oligactis Pallas—Michigan.*
Our fresh-water sponges are few in kinds, but often grow in great luxuriance. 281