posterior antennae are on the whole more strongly built than in the Calanoida, 

 and are generally tipped with coarse denticulated spines. They always carry a 

 secondary appendage (outer ramus ) ; but in most cases this appendage is of rather 

 inferior size as compared with the chief stem (the inner ramus). The mandibles 

 carry outside a more or less developed palp, and this is also generally the case 

 with the maxillae. The anterior maxillipeds are short and stout, with several 

 digitiform processes, the number of which may however be considerably reduced. 

 The posterior maxillipeds in the majority of forms are pronouncedly prehensile, 

 terminating in a powerful clawed hand. There are, however, a number of forms 

 in which these appendages are of a very different structure, and not prehensile 

 at all. The 1st pair of legs are in some instances of a structure similar to that 

 of the succeeding pairs; but in the majority of cases they differ rather conspicu- 

 ously, being more or less transformed into grasping organs. The 3 succeeding 

 pairs are always natatory and generally have both rami 3-articulate, though the 

 inner one may sometimes be much reduced in size. The last pair of legs are 

 very unlike the others, and are never natatory. They are generally lamellar in 

 structure, biarticulate, and edged with strong setse or spines. 



The ova are in most cases carried within a single ovisac attached to the 

 ventral face of the 1st caudal segment. More rarely 2 ovisacs are present, which 

 likewise are appended to the ventral face, never, as in the Cyclopoida, laterally 

 or subdorsally. 



With regard to the inner organisation, it may be noted that, unlike what 

 is the case in the Calanoida, no heart is present (except in the genus Mis&phria), 

 and that the male genital apparatus is always perfectly symmetrical. 



By far the greater majority of forms belonging to the present group are 

 marine, only a very limited number of genera being represented in fresh water. 

 Some species seem, however, to prefer brackish water, and so far cannot properly 

 be said to be either true marine or true fresh-water forms. Contrary to what is 

 generally the case with the Calanoida, the Harpacticoida are, as a rule, true 

 bottom forms, to be sought for among algse near the shores, in tidal pools, or in 

 mud brought up from various depths. But in this respect also there are some 

 exceptions. Thus the species of the genera Setella, Euterpe, Clytemnestra, Mi- 

 1'iK-ia, lead a true pelagic life. Some few forms are known to be commensal 

 with other Crustacea (Sunaristes), or even with Vertebrates (Balcmiopliilus) ; but 

 no true parasites are as yet known among the Harpacticoida. 



The several families comprised within the present group may be arranged 

 under 2 chief sections. In the one, Achirota, the posterior maxillipeds are of 

 weak consistency and not prehensile; in the 2nd, Chirognatha, these appendages 



