Capt. DuCanc on the Metamorphosis of Crustacea. 1 79 



of the parts of the adult animal than an actual metamor- 

 phosis. 



The drawings Nos. 1 and 2 represent the appearance of the 

 larva on its first exclusion from the egg, and excepting in 

 being more accurately drawn, I am happy to find that they 

 do not differ materially from the hasty sketches I had an op- 

 portunity of making last year at the end of the third day. 

 No. 1. shows the animal as it appears in motion in the water ; 

 No. 2. as viewed when lying on its back, in which position 

 the rudiments of the true legs are visible, doubled up under 

 the thorax. 



No. 3. is the larva in its second stage, ascertained by ob- 

 serving the moult of the former. It has now one serrature on 

 the dorsum of the cephalothorax : the eyes have become pe- 

 dunculate. It has five pairs of natatory legs ; and its proper 

 legs, both walking and prehensile, are developed : the rudi- 

 ments of subabdominal fins are becoming visible, but the tail 

 continues spatulate as before. 



No. 4. is its third stage, also ascertained by witnessing the 

 moult. The larva has now two serratures or spines on the 

 cephalothorax, the legs are the same as in the second stage ; 

 but the subabdominal fins are more developed, and the tail 

 has acquired two leaflets on each side, one of them being de- 

 licately fringed, the other still only in a rudimental state. 



Nos. 5. and 6. represent the larva in its fourth or last stage, 

 as it appears swimming in the water and lying on its side. I 

 have however not had an opportunity of observing the moult 

 in this case. It is evidently the same animal as is drawn by 

 Mr. Thompson in Jameson's < Edinburgh Journal 5 for July 

 1836. The larva has now three serratures, six pairs of false or 

 natatory legs, and the true legs resemble those of the full-grown 

 or perfect prawn; the subabdominal fins are still further deve- 

 loped, and the tail also approaches nearly to that of the adult 

 animal, which I had the satisfaction of observing in the con- 

 dition its next moult brings it to. It then becomes a true P«- 

 Icemon. 



It is a curious and interesting circumstance in tracing the 

 changes of this larva to observe, that through all its conditions 

 its movements are retrograde ; but no sooner has it divested 



N 2 



