Whether _Pent. denticulatum_ be or be not devoid of clinical interest, it is quite clear from Aitken’s account that _P. constrictum_ is a formidable parasite and one that occasionally proves fatal to the bearer. As his remarks suggest, a parasite that can produce both pneumonia and peritonitis is not a creature that either the physician or the sanitarian can afford to ignore. Lastly, I must again express my belief that the so-called _Echinorhynchus_, described by Welch, if it be not the _Pentastoma denticulatum_, must either be referred to _P. constrictum_ (in an early larval condition), or to some other hitherto undescribed pentastomatoid larva. BIBLIOGRAPHY (No. 37).--_Aitken, W._, “On the occurrence of _Pentastoma constrictum_ in the Human Body as a cause of painful Disease and Death,” repr. from the ‘Science and Practice of Medicine,’ 4th edit., 1865.--_Bellingham_, in ‘Ann. Nat. Hist.,’ vol. xiv, p. 162.--_Blanchard_, in ‘Ann. des Sci. Nat.,’ ser. 3, t. viii, and in ‘Règn. Anim.’ (with figs.).--_Cobbold_, ‘Entoz.,’ p. 393 _et seq._--_Idem_, in ‘Quart. Journ. Med. Sci.,’ 1859, p. 205.--_Idem_ (“_P. cephalophi_”), in ‘Linn. Trans.,’ xxii, p. 357, and xxiii, p. 350.--_Idem_, in ‘Zool. Soc. Proc.,’ 1861, p. 124.--_Diesing_, ‘Syst.,’ i, p. 609.--Idem, ‘Revis. der Cephalocot.,’ s. 327.--_Frerichs_ (l. c., in text), vol. ii, p. 276.--_Klob_ (und _Schroff_), in ‘Gesellsch. d. Aerzte,’ Wien, 1860.--_Küchenmeister_, l. c., i, s. 370, Eng. edit., tab. viii.--_Idem_ (with _Van Beneden_), in ‘Bullet. Acad. Belg.,’ xxii (with figs.), 1855.--_Landon_ (quoted in text).--_Leuckart_, in ‘Zeitsch. f. rat. Med.,’ 1857; see also “Obs. on the development and early condition of the _Pent. tænioides_,” in ‘Ann. Nat. Hist.,’ vol. iii, 3rd series, 1859; also my translation of his “Further Observations on the development of _P. tænioides_,” from ‘Henle and Pfeufer’s Zeitsch.,’ in the ‘Quart. Journ. of Micr. Sci.’ for 1859.--_Idem_, ‘Bau und Entwicklungsgeschichte der Pentastomen, nach Untersuchungen besonders von _P. tænioides_ und _P. denticulatum_,’ Leipzig, 1860.--_Moquin-Tandon_, ‘Med. Zool.’ (Hulme’s edit.), “The Linguatula,” p. 329.--_Pruner_ (“Nematoideum”) in ‘Krankh. d. Orient.,’ 1847.--_Schubart_, ‘S. und K. Zeitschr.,’ Bd. iv.--_Welch_, see Bibl. No. 36.--_Zenker_, in ‘H. und Pf. Zeitschr. f. rat. Med.,’ 1854, s. 212 (with figs.). [Illustration: FIG. 53.--_Demodex folliculorum_, var. _caninus_. _a_, Female; _b_, male. Viewed from below and in profile. Magnified 300 diameters. After Mégnin.]