POST-LARVAL STAGES OF JASUS LALANDTI. 105 



flagellate branch was the exopodite, but this was clearly seen not to be the 

 case, as in some specimens the non-flagellate branch still possessed the 

 indentations o£ the swimming setse. A certain amount of torsion therefore 

 takes place in the antenna when it comes to take up a more anteriorly- 

 directed position in the phyllosoma. 



The mandible (fig. 15, md.) now shows more clearly the outer tridentate 

 spine, followed by a ridge of spines passing inward, and separated by an 

 interval from a raised portion provided with small short spines. This 

 arrangement does not seem to differ from that in the larger phyllosomas. 



The first maxilla (fig. 15, mx. 1) consists of a short, stout, basal part, 

 inserted immediately behind the base of the mandible. Its two short 

 branches are each provided with two long, stout, and curved setse, on which 

 are secondary setse, giving them a plumose appearance. In shed cuticles 

 the cleft between the two branches is seen to be much deeper than appears 

 in the complete animal, and a basal part can hardly be recognised. They 

 are commonly regarded as two segments of the protopodite. 



The second maxilla (fig. 15, m.v. 2) is about '11 mm. in length, blade-like, 

 and usually shows no division. It is attached to the body by a relatively 

 narrow base, but soon broadens out into a flat expansion, the posterior border 

 of which is straighter than the anterior, which is provided with a single 

 spine about half the diameter of the blade, and situated at about the middle 

 of its length. The appendage ends in a knob-like projection, provided with 

 four very long plumose spines, about double the length of the appendage. 

 This little knob is of interest, as it is destined to become the scaphognathite. 

 In some specimens it is clearly defined by a constriction at its base. 



The first maxillijjede (fig. 15, mxp. 1) is very small, and consists of a little 

 hillock-like projection about '006 mm. in diameter and height. It has a 

 long spine projecting from its apex, as in the naupliosoma stage, and, in fact, 

 has not apparently altered. It is to be noted that it is here well separated 

 from the base of the second maxilla, for, when it reappears after an apparent 

 absence in the next stage, it occupies a different position. 



The second maxillipede (PL 13. fig. 16) consists of five distinct segments. 

 The first is short, the second about four times its length, the third equal to 

 it, the fourth slightly longer and somewhat larger than the last. There are 

 no spines on the first and third, but on the second there is a well-marked 

 one, about the middle of its length. At the distal extremity of the fourth 

 there are five long spines, each provided with spinules on its inner side. 

 The last segment is terminated by a long curved spine devoid of spinules. 

 At its base are four small spines. The whole appendage reaches to about 

 the anterior third of the head region. 



The third maxillipede (fig. 17) consists of six distinct segments, the first 

 short and provided with a long broad spine, directed downwards and inwards. 

 The second segment is long, and has two or three spines at its distal end, but 



