230 T>'R- J. D. F. GILCHRIST ON A FEEE-SWIMMING 



development and transition into the phyllostoma stage described. In both 

 cases the form which emerges from the egg is a typical phyllosoma, the 

 body is clear and transparent, the limbs are fully expanded, the various spines 

 and swimming-setge are fully developed. In the newly-hatched larva of 

 Palinurus (Jasus) lalcmdii, on the other hand, it is not till the next moult 

 that the typical phyllosoma-form is assumed and in the first free larva the 

 cephalic region is still opaque owing to the presence of yolk, the thoracic 

 limbs with their spines and swimming-setse are not fully developed. In 

 reo-ard to these points, therefore, the naupliosoma larva corresponds to a 

 stao-e passed in the egg in the case of Sct/llarus and the northern Palinurus. 



Again, in Palinurns quadricornis and Scyllarus the second antennae at the 

 time of hatching are shorter than the first, whereas in the form under 

 consideration the first are markedly the shorter, being only about three- 

 fourths of the length of the second antennee. This new form further differs 

 from the young P. quadricornis in having well-marked biramose antennse, 

 in this respect resembling Scyllarus. The presence or absence of marked 

 biramose antennae cannot therefore be taken as a means of distinguishing the 

 larval forms of the Palinuridse from other similar forms. This biramose con- 

 dition persists in the succeeding phyllosoma stages of the Cape Palinurus, 

 and is marked in the oldest undoubted phyllosoma belonging to it which 

 I have yet found (4-4 mm. in length). 



The hepatic diverticula of the naupliosoma have a much greater resem- 

 blance to those of the phyllosoma of Scyllarus than to that of P. quadricornis, 

 there being three pairs in the first two, while, in the last, they are numerous 

 from the very beginning. 



An agreement between the first two is also seen in the absence of an 

 exopodite in the third maxilliped, while it is present in the youngest 

 phyllosoma of the last (taken from the egg just before hatching). 



in the newly hatched larva of Scyllarus the 4th and 5th ambulatory legs 

 are scarcely to be seen, while in that of P. quadricornis they occur as minute 

 buds. In the naupliosoma there is only a slight trace of the 4th, in the form 

 of a minute bud, while no traces at all of the 5th were observed, though they 

 both appear in the stage of 4*4 mm. 



Neither in Scyllarus nor in P. quadricornis are the antennae at any stage 

 provided with long setose swimming-processes as in the naupliosoma. It is 

 presumed tha', at one stage in its phylogeny, Paliymrus had a free nauplius 

 stage, whose chief organs of locomotion were the biramose antennae and their 

 swimmino- cuticular processes. The appearance of such organs at this late 

 stage in the Gii^Q Palinurus maybe a new acquisition or a belated appearance 

 of an old. 



The significance of this stage of so short duration in the life-history of the 

 Crawfish appears to be that it enables the young to ascend more rapidly, and 

 with more certainty, to the surface than in the case with the slowly moving 



