V. ANNELID PARASITES. SUCTORIA.--In this category one must place all such suctorial annelids as affix themselves to hosts for a longer or shorter period. Many of the leech-like parasites (_Clepsinidæ_, and especially _Malacobdellidæ_) remind one of certain flukes (_Tristoma_, &c.) possessing ectozoal habits; whilst the leeches, properly so called, afford instances of the passage from a semi-parasitic to what has been called the free parasitic mode of existence. In tropical countries these creatures very readily attach themselves to man and animals, often creating severe distress. The genera _Clepsine_ and _Hæmocharis_ attack mollusks and fishes respectively. The species are all ectoparasitic and exceedingly numerous. They cannot be described in this work. VI. ARACHNID PARASITES, ARACHNIDA (part of).--The great class of articulated, limb-jointed, or, more strictly, arthropodous animals, includes a variety of parasites. The mites, true ticks, and such like creatures, belong to this group. Some few of them are entozoal in habit, others are only partially so, whilst the majority are entirely ectozoal. Of the two great sections of Arachnida, namely, Pulmonaria and Trachearia, the latter alone contains strictly parasitic forms. The parasitic species belong to the following families:--_Pentastomidæ_, _Pycnogonidæ_, _Ixodidæ_, _Acaridæ_, _Gamasidæ_, _Hydrachnidæ_, _Solpugidæ_. The parasitism of some of the species is very partial or slight. Thus, certain of the water mites, in their juvenile state, dwell on aquatic insects only; and the tick-like _Gamasidæ_ occur upon dung-beetles. The other ectozoal species attack vertebrated animals, and several attach themselves to man himself. The whale lice (_Cyamidæ_) are here included in the _Pycnogonidæ_, though often placed by zoologists with the Crustaceans. VII. CRUSTACEAN PARASITES. CRUSTACEA (part of).--A large number of species belonging to various well-marked sections of this great class of Invertebrates are parasitic in their habits, most of them being comprised in the so-called haustellated group. They are familiarly known to zoologists as Epizoa. As this latter term implies, they are strictly ectozoal in character, most of the species victimising fishes by attaching themselves, not only to the general surface of the body, but also to the eyes, and especially to the gills or branchiæ. The species for the most part belong to the families _Lernæidæ_, _Caligidæ_, _Dichelestidæ_, and _Argulidæ_. In this category must likewise be placed two other families belonging to the so-called isopodous section of edriophthalmatous crustaceans. These are the _Cymothoidæ_, which attach themselves to the tails of fishes, and the _Bopyridæ_, which occupy the branchial cavity of shrimps. The nature of this work precludes any detailed notice of the numerous members of this section.