P. 31, line 6 from bottom: _delete_ “human,” as Leidy really worked with _Endamœba blattæ_, parasitic in the gut of the cockroach. P. 43, line 12 from bottom: _for_ “John’s” _read_ “Johns.” P. 44, line 13 from bottom: _for_ “_Amœba buccalis_, Sternberg,” _read_ “_Amœba buccalis_, Steinberg.” P. 46, line 13 from top: _for_ “breath” _read_ “breadth.” P. 53, In footnote ^1, line 6 from bottom: _insert_ “see” before _Arch. f. Protistenk_. P. 75: To paragraph regarding development of the parasite in the fly’s salivary glands, _add_ that the crithidial phase takes two to five days. P. 111, line 8 from top: the date of Sangiorgi should be 1911. P. 142, line 7 from top: _insert_ “Genus.” before *Eimeria*. P. 252, _Insert_ heading “Family. *Opisthorchiidæ*, Braun, 1901,” _above_ “Sub-family. *Opisthorchiinæ*, Looss, 1899.” P. 351, description of fig. 255, line 3: _for_ “Thoma” _read_ “Thomas.” P. 471, line 15 from bottom: _for_ “alcohol 100 parts” _read_ “alcohol 100 c.c.” P. 472, line 11 from bottom: _for_ “Or (2) 10 _per cent. formalin_,” _read_ “Or (2) _fix in hot_ 10 _per cent. formalin_.” P. 493, line 21 from top: _for_ “Conoy” _read_ “Couvy.” P. 589, line 2 from top: _for_ “*carnosa*” _read_ “*carnaria*.” P. 620, line 15 from top: _for_ “fo” _read_ “of.” P. 622, line 12 from bottom: _delete_ comma after quantity. P. 626, line 6 from bottom: _delete_ comma after Mackie (1915). P. 638: _insert_ title “*TREMATODES*” above that of “Fascioliasis.” P. 709, line 9 from bottom: _omit_ second Pediculus capitis. P. 748, line 8 from top: _for_ “cytologica” _read_ “cytological.” P. 753, line 4 from bottom: _for_ “*Fercocercous*” _read_ “*Furcocercous*.” P. 755 line 7: _for_ “*Oncocerca*” _read_ “*Onchocerca*.” ON PARASITES IN GENERAL. By the term PARASITES is understood living organisms which, for the purpose of procuring food, take up their abode, temporarily or permanently, on or within other living organisms. There are both plants and animals (Phytoparasites and Zoöparasites) which lead a parasitic life in or upon other plants and other animals. Phytoparasites are not included in the following descriptions of the forms of parasitism, but a very large number of animal parasites (zoöparasites) are described. The number of the latter, as a rule, is very much underrated. How great a number of animal parasites exists may be gathered from the fact that all classes of animals are subject to them. Some of the larger groups, such as _Sporozoa_, _Cestoda_, _Trematoda_ and _Acanthocephala_, consist entirely of parasitic species, and parasitism even occurs among the vertebrates (_Myxine_). It therefore follows that the characteristics of parasites lie, not in their structure, but in the manner of their existence.