A recently published paper, ‘The Jump of the Flea: a Study of the Energetics and a Model of the Mechanism’, by H. C. Bennet-Clark and E. C. A. Lucey, J. Exp. Biol . (1967), 47, 59-76 contains several errors which the authors wish to correct. These are as follows: Page 62, formula one, should read s = v 2 /2 ft. and the calculation that follows assumes that it is as stated here. Page 74, table one, has a spacing error and should read: Pulex irritans 0.49 4.1 x 10 -4 12 2.2 m. 16 Preserved ♀ --* 5.3 x 10 -4 16 --* Up to 20 cm. Page 74, line 6, substitute for classes, cases. We are grateful to the Hon. Miriam Rothschild for bringing various points in the section on materials, page 59, to our attention and we offer the following corrections: (i) Materials, line one: for cuniculus read cuniculi. (ii) Line four: delete generally supposed to be the more primitive superfamily. (iii) Lines 5 and 6: delete presence of internal skeletal rods on the metapleuron but not on the mesopleuron (Rothschild & Hopkins, 1953) and substitute, absence of an outer internal ridge on the mid coxa (Hopkins & Rothschild, 1953). (iv) Page 76: reference to Rothschild M. & Hopkins G. H. E. should read Hopkins G. H. E. & Rothschild M. and be placed after the second reference. These corrections in no way affect the argument that follows; our present concern is to offer our humble apologies for having mis-represented these authors and for any embarrassment that this may have caused.