276 



CRUSTACEA. 



Fjg. 12G.— Larva 01 the American lobster, just 

 hatched (after Smith). «', first, a", second 

 antenna; in/"', third maxillipede ; pf-p^, first 

 five ambulatory limbs. 



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

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

 leaves the egg (Fig. 126) is the Mysis stage, which moves about by 

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

 the five pairs of ambulatory limbs (mf'"-p y ) 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 limb- 

 rudiments. The telson is a 

 triangular toothed plate, in- 

 dented posteriorly. The first 

 antenna (a) is still un jointed, 

 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. 

 The 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 pineer- 

 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 well 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 

 lust. The exopodites of the ambulatory limbs are mere vesti 

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

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



