Until lately not very much attention had been paid to the parasites of bats, probably on account of the insignificance of the hosts. However, whilst Dr Dobson has recently been extending the subject of Cheiropterology, Prof. van Beneden has added largely to our knowledge of the parasites of bats. In his beautiful memoir, the Belgian helminthologist asks whether the parasites quit their hosts during the period of hybernation, and then proceeds to answer that question in the negative. Should the bats die, the parasites of necessity share the same fate. It would appear, however, that the spermatozoa of the worms are capable of surviving their parents for a fortnight or even longer. Flukes abound; the most common species (_Distoma lima_) infesting the pipistrelle, noctule, mouse-colored bat, Natterer’s bat, parti-colored bat, Daubenton’s bat, whiskered bat, and the greater and lesser horseshoe bats. Almost as abundant is the _Distoma chilostomum_ found in most of these bats, and also in Leisler’s or the hairy-armed bat. Dujardin’s _D. heteroporum_ is a synonym of the species. Schreber’s _Monostomum_ is probably identical with Van Beneden’s _Distoma ascidia_. This fluke he found in _Vespertilio marinus_, _V. dasycnemus_, _V. Daubentonii_, _V. emarginatus_, _V. serotinus_, _V. mystacinus_, _V. pipistrellus_, _V. auritus_, and in _Rhinolophus hippocrepis_. Another species, distinguished from _D. ascidia_ by its large ventral sucker, has been found in great numbers in the noctule (_D. ascidioïdes_, Van Beneden). The cestodes of bats are not numerous. The best known species (_Tænia obtusata_) has been found in the serotine, in the mouse-colored bat, and in _Vespertilio lasiurus_. Another species (_T. decipiens_) occurs in _Molossus perotis_, and _Chylonycteris rubiginosus_, and a scolex, forming the type of a new genus and species (_Milina grisea_, Van Ben.) has been obtained by hundreds in the intestines of _Vesp. murinus_ and _V. serotinus_. Of nematodes we have _Ophiostomum mucronatum_, Rud., and _Oph. spinosum_, W.-Suhm (from _Vespertilio mystacinus_)., _Trichosomum speciosum_, Van Ben., _Strongylus tipula_, Van Ben., _Strongylacantha glycyrrhiza_, Van Ben., _Litosoma filaria_, Van Ben., _Ascarops minuta_, Van Ben., and one or two sexually-immature forms, either found loose in the tissues or occupying cysts. The Acanthocephala are not known to infest bats. Respecting insects, one family (Nycteribiidæ) is exclusively parasitic upon bats. They resemble the forest-flies in their habits. The best known species is _Nycteribia Latreillei_, but several others (_N. biarticulata_ and _N. Sykesii_, Westw.) have been described. One or more of the Brazilian bats are infested by _Lipoptena phyllostomatis_, Nitsch, and Westwood has obtained several allied forms of _Hipposcidæ_ (of the genus _Strebla_), also from bats. As regards the true Arachnidans (mites and ticks), Van Beneden enumerates _Ixodes lividus_, Van Ben., _Pteroptus vespertilionis_ and _P.