A FEEE-SWIMMING NAUPLIOID STAGE IN PALINUEUS. 225 



A Free-swimming Nauplioicl Stage in Pcdhmrus. 

 By J. D. F. Gilchrist, M.A., D.Sc, Ph.D., F.L.S. (With 1 Text-figure.) 



[Read 3rd April, 1913.] 



The hirva of Palinurus, ScyUarus, and the Loricata generally has hitherto 

 been supposed to hatch out from the egg in the form of a " phyllosoma," 

 characterised by a flattened transparent body and the presence of swimming- 

 organs, in the form of the exopodites of some of the thoracic appendages. 



A number of observations, which I have made on the early stages of 

 Palinurus (Jasus) lalandU, seems to indicate that this is not so in the case 

 of this South African Crawfish. 



The observations were made on a number of specimens of this crustacean 

 kept alive in tanks at the Marine Laboratory at St. James, near Cape Town. 

 They are hardy animals, and can be kept in good condition for a considerable 

 length of time without much trouble. On hatching, the larvse are given off 

 in large numbers, and are readily seen by the naked eye in the typical 

 phyllosoma stage. Among these slowly -moving larvse was observed a 

 number of nauplius-like forms, with large biramose antennse, by means of 

 which they rose to the surface in a series of rapid dancing movements. 

 These larv?e on closer examination proved to be, not nauplii, but the earliest 

 free stage, differing considerably from a phyllosoma. The duration of this 

 stage is A^ery brief (4-6 hours), and is readily overlooked_, especially if 

 hatching takes place during the night. 



In the advanced egg, which measures about 0*7 mm. in breadth and slightly 

 more in length, the embryo is seen to have the body so bent on itself that 

 the thoracic appendages are compactly folded up over the ventral aspect of 

 the body, passing between the eyes, and extend to some considerable distance 

 over the back of the cephalic region. The antennse are well developed, are 

 longei' than the antennules, and biramose ; they are folded over the back of 

 the embryo, and their long feathery swimming-setse overlap each other in 

 this region. 



On hatching, the embryo leaves the egg, and, at the same time, throws off 

 the old cuticle, which may sometimes be seen lying alongside of or near the 

 ruptured egg. The antennse and antennules immediately expand, while the 

 other appendages still retain their folded position. Thus the larva at this 

 stage appears to have a rounded or ovoid body, consisting of cephalic and 

 thoracic regions bent over on each other, the short abdomen and long- 

 appendages being folded up ventrally. A little later in this stage, the 

 appendages become somewhat unfolded, and the angle of flexure between the 



