NAUPLIOID STAGE IN PALINURUS. 227 



cephalic and thoracic regions becomes less acute, so as to give the whole body 

 a more elongate appearance. This unfolding also occurs in specimens placed 

 in preserving-fluid at this stage. 



The superficial resemblance to a nauplius at this stage is striking, especially 

 in the large bi ramose swimming-antennse and apparently ovate body, but a 

 closer examination of the body and appendages indicates that the larva is 

 much more advanced in organization than a nauplius, this latter stage having 

 presumably been passed through much earlier in the development of the egg. 

 For convenience the larva mny be called a naupliosoma or described as being 

 in a nau{)liosoma stage. 



The cephalic region is broad (0-72 mm.), and is almost circular in outline, 

 the length, from the anterior to the posterior margin of the cephalic shield, 

 being about equal to its breadth. This region is not flat and transparent, as 

 in the succeeding phyllosoma stages, its depth (from the centre of the back 

 to the mouth-appendages) being about four-fifths of its breadth, nor is it 

 transparent, being as yet filled with a considerable amount of yellow yolk- 

 granules. The antennal glands, which appear distinctly in the next stage, 

 were seen in some, and also three large hepatic diverticula on each side. 

 Two powerful muscles, which degenerate at a later stage, were observed 

 attached to the base of each of the antennae. The cephalic shield is rounded 

 dorsally, and extends backwards over the thoracic region to about the anterior 

 margin of the base of the second maxillipeds (in some cases only to the first 

 maxillipedj. 



The tJioracic region is bent forward and under the cephalic region, there 

 being, especially at first, a somewhat abrupt flexure of the body at the 

 junction between the two. This region is characterised also by the presence 

 of a well-marked segment — that to which the first maxilliped belonos — 

 which appendage, it is to be noted, is a mere rudiment. The thoracic region 

 is narrow, resembling the body of a pycnogonid, and, except the part 

 mentioned, show^s no distinct traces of segmentation. It is transparent 

 except for the presence of a thin yellow streak — the remains of the yolk in 

 the intestine. 



The abdominal region or tail is short, and, like the thoracic region, is flexed 

 ventrally. In its anterior two-thirds four distinct segments can be dis- 

 tinguished. It is also narrow, scarcely exceeding the breadth of the first 

 joint of the last appendage (the sixth thoracic). It ends in a pair of furcal 

 processes;, provided with setse, which are not yet free, but covered over 

 by cuticle. 



The ^yigmentation of the body is striking; the cephalic region and the 

 intestine are of a faint yellow colour from the presence of the yolk, while on 

 the body and limbs are bright blood-red patches of pigment, usually of a 

 stellate structure in the living animal. These are disposed as follows : 



LINN. JOURN. — ZOOLOGY, VOL. XXXII. 19 



