_E. clavula_ Duj. is found in _Salmo fario_, _Abramis brama_, _Cyprinus carpio_, _Gobius niger_, _Lepadogaster gouanii_, etc.; _E. linstowi_ Ham. in _Leuciscus idus_, _Abramis ballerus_, _Abramis bipunctatus_, and _Acipenser huso_; _E. lutzii_ Ham. was found by Dr. Lutz in Brazil in the intestine of _Bufo agua_; _E. angustatus_ Rud. occurs in such numbers in the perch, _Perca fluviatilis_, as to almost occlude the lumen of the intestine, and one out of every three or four fish in certain districts is infested by it. It is also found in the pike, _Esox lucius_, and the barbel, _Barbus vulgaris_. The first or larval host of this species is the Isopod _Asellus aquaticus_. _E. moniliformis_ Brews. is stated to attain maturity in the human intestine. Except for the fact that _G. gigas_ has once been observed in the same place, this is the only human parasite amongst the Acanthocephala. Its normal second hosts are _Mus decumanus_ and _Myoxus quercinus_, and its first or larval host, the larvae of the beetle _Blaps mucronata_. _E. porrigens_ Rud. is found in considerable numbers in the small intestine of a fin-whale (_Balaenoptera sibbaldii_), and _E. strumosus_ Rud., in the small intestine of a seal (_Phoca vitulina_), and in the body-cavity of the angler fish (_Lophius piscatorius_). _E. acus_ is common in the whiting, _Gadus merlangus_. FAMILY II. GIGANTORHYNCHIDAE.—Large forms with ringed, flattened, and _Taenia_-like bodies. The hook-papillae are covered all over with transparent chitinous sheaths with two root-like processes. The proboscis-sheath is muscular and without a lumen. The central nervous system is excentrically placed below the middle of the so-called sheath. The lemnisci are long twisted tubes with a central canal. {184}Hamann places three species in this family: _Gigantorhynchus echinodiscus_, _G. spira_, and _G. taenioides_; but as he points out that _E. gigas_ resembles these in its more important structural features, it seems advisable to include it here under the name _G. gigas_. The members of the first family often present a transversely ringed appearance after death, but the Gigantorhynchidae are ringed when alive, and the circular canals in the skin show a certain regularity, being arranged one between each two rings. There is no lumen in the proboscis-sheath, which is not attached to the boundary between the proboscis and the trunk, but to the inner surface of the proboscis, and the whole can be retracted within the anterior portion of the body, which is invaginable. There are always eight cement-glands, and other differences exist in the musculature, hooks, and position of the nervous system.