22 PEOF. M. M. HAETOG OX THE 



The month (PI. I. figs. 12, 13 ; PL III. figs. 1, 4, G, mo.) is bounded by the lahriim iu 

 front, by il^n postoml bar behind, by the socket and base of the mandibles at the side, 

 and ventral to them hy the paragnathcs and maxillce, which also in adduction form its 

 ventral limit. 



The labrum (PI. I. figs. 11, 12 ; PI. III. fig. 4) is a broad plate continuous with the epistoma, 

 inclined backwards and downwards and bevelled at the angles ; its free margin ends in 

 a row of eight teetli inclined to the median line and larger as they are more external ; 

 outside each of the external teeth is another, smaller, and then, separated by a short 

 space, inclined upwards and outwards is another large tooth. 



On the anterior aspect, i. e. external, are two longitudinal rounded ridges bearing a 

 ti'ansverse row of long curved sette turned downwards and forwards, like a moustache, 

 overhanging the toothed edge. The inner, posterior, or oral face bears just above the 

 teeth a fine transverse ridge of chitin, some way above which is a median circular pore, 

 the opening of the saUvurij duct (PI. III. fig. 6, sa. p.). The labrum must be raised to 

 close the mouth by the action of the anterior divaricators of the gullet, and returns to its 

 former position by elasticity. 



The paragnath(s (PI. I. figs. 12, 13, 14; PI. III. figs. 5, 6,jj^.) (Clans) are two processes 

 running forwards below the shafts of the mandibles from the jwstoral bar, together with 

 which they form the " bilobed metastoma" of Huxley. They have a very irregular shape, 

 as will be seen by the figures ; and either bears on its ventral outer edge a row of fine 

 setse, internal to this a row of teeth, and one or two isolated teeth, and on its inner 

 side a transverse plate (pectinate process) flattened from before backwards, and incised into 

 a number of strong teeth lying behind and parallel with the plates of the mandibles. 

 The paragnathfB are attached to the outer angles of the postoral bar, where it joins the 

 inner arthrodial ridge between the sockets of the mandibles and maxillae. This bar is 

 prolonged inwards and backwards at its middle into a short apodeme, receiving the 

 insertions of four muscular slips [retractors of the postoral bar) (PL III. figs. 4, 5, m. r. 

 poh.) which run downwards and forwards from their origin on the lower surface of the 

 free entosternite, perforating the ventral nerve-cord in two collateral pairs ; this draws 

 the postoral bar into a V, the result being the approximation of the paragnatha? under 

 the mouth, and the meeting of their toothed plates ; while adduction is due simply to the 

 elasticity of the postoral bar. Thus the oral cavity is a hollow wedge with a squarish 

 base rapidly narrowing above and in front of the gullet, which, Avheu closed, has its 

 anterior and posterior walls approximated so as to form a slit. The upper parts of the 

 mouth are covered with transverse rows of very fine, short, close-set seta?, which probably 

 exist also in the gullet*. 



The anterior wall of the mouth contains incomplete semicircular constrictors, transverse 

 muscular strips (PL III. fig. 6, m. cons. or.). In their intervals are inserted,. by brush-like 

 diverging ends abutting directly against the cuticle, the anterior apertors of the mouth 



* I may note here that food, in Cyclops and tho other members of Ci/clopidcf, and llarpactkidce, is directl)- put into 

 the mouth bj' the appendages, not whirled in by the vortices they produce (as writers have repeatedly stated), for 

 the simple reason that they are not capable of producing vortices. The statement is correct as regards Diaptomus and 

 probably all the Calanidce, 



