276 



CRUSTACEA. 



Fjc. 12G. — Larva ot the American lobster, just 

 liatched (after Smith), a', first, a", second 

 antenna ; in/'", third niaxillipede ; i^^-p^, first 

 five ambulatory limbs. 



l)y the works of Kroyer (No. 136), G. 0. Sars (No. 148), S. J. 

 Smith (No. 153), and Ryder (No. 147), the stage at which the young 

 leaves the egg (Fig. 126) is the My><is stage, which moves about by 

 means of the exopodites of the third pair of maxillipedes and of 

 tlie five pairs of ambulatory limbs {mf"'-p'') developed as strong 



swimming organs. The dorsal 

 shield passes anteriorly into 

 a simple rostrum. The ab- 

 domen is distinguished by 

 the presence on its segments 

 of dorsal and lateral spines^ 

 but is still devoid of linil)- 

 rudiments. The telson is a 

 triangular toothed plate, in- 

 dented posteriorly. The first 

 antenna (a') is still unjointed, 

 the second (a") is biramose, 

 with an exopodite changed 

 into a scale and a slender 

 endopodite (rudiment of the 

 flagellum). The mandible- 

 carries a three-jointed palp, there is no exopodite on the first maxilla. 

 Tlie second maxilla and the maxillipedes resemble in essentials those 

 of the adult, but are still in many respects rudimentary. The 

 endopodites of the three anterior pairs of ambulatory limbs already 

 terminate in rudimentary pincers. 



In the next stage, the limb-buds appear on the second, third, 

 fourth, and fifth abdominal segments. On the first antenna, the 

 segmentation of the principal flagellum and the rudiment of the 

 accessory flagellum can already be recognised. The three anterior 

 pairs of ambulatory limbs have increased in size, and the pincer- 

 rudiments are more clearly developed. 



In the third larval stage, the Schizopodan features gradually dis- 

 appear, while the adult characters begin to develop. The exopodite 

 of the third maxillipede, as Avell as that of the fifth ambulatory 

 limb, degenerate, while the limbs of the sixth abdominal segment 

 attain development. The abdominal spines begin to degenerate. 



In the next stage, the Schizopodan characters have been entirely 

 lost. The exopodites of the ambulatory limbs are mere vestiges. 

 The larva, in all essentials, resembles the adult, but still retains its 

 pelagic manner of life, and swims by means of its abdominal limbs. 



