v CRUSTACEA ONTOGENY 395 



Development of Palinurus and Scyllarus (Decapoda, Macrura, Fam. Loricata). 



The early larval development is carried on within the shell ; during this 

 development 2 stages, a Nauplius stage and a very important further stage which 

 might be called the embryonic Phyllosoma stage, are passed through. The 

 characteristics of this latter stage are as follows : There are 2 pairs of antennae, 

 mandibles, and 2 pairs of maxillse. The thoracic limbs have all begun to form, i.e. 

 3 pairs of maxillipedes and 5 pairs of ambulatory limbs. The 2 most posterior 

 (ambulatory limbs) are only present as minute buds. The 6 anterior are biramose, 

 but the exopodites of the 2d and 3d pairs of maxillipedes are degenerated even 

 during embryonic life. There are two stalked lateral eyes, and the median Nauplius 

 eye. In the body 3 regions are to be distinguished. (1) Head with dorsal shield ; 

 (2) thoracic region, in which the segmentation is indicated ; (3) a distinctly segmented 

 but limbless abdominal region ending in a fork. 



Before the larva is hatched, however, in addition to the 2 posterior pairs of 

 ambulatory feet which remained undeveloped, the 1st pair of maxillipedes dis- 

 appear, and the 2d pair of maxillse and the 2d pair of antennae degenerate. 



FIG. 26G. Phyllosoma of Palinurus (after Glaus), ad, Abdomen ; I, liver. 



In the larva hatched from the egg the above-mentioned regions of the body can be 

 recognised it is much flattened dorso-ventrally (like a leaf), and as transparent as 

 glass ; it is called the younger Phyllosoma (Fig. 266). 



The older Phyllosoma larva is distinguished from the younger by the following 

 characteristics. The 1st pair of maxillipedes has formed anew, and the 2 posterior 

 pairs of ambulatory feet have developed. The 2 posterior maxillipedes again develop 

 exopodites, and on the ambulatory limbs the rudiments of the gills appear. The 

 abdomen is more elongated and shows the rudiments of the pleopoda. The larva 

 thus already has, apart from its strange form, typical Decapodan characteristics. 

 Its transformation into the sexual form has not been observed. 



In the development of the Loricata we note : 



1. That during the processes which go on in the last part of embryonic 

 life the body with its extremities becomes differentiated typically from before 

 backward. 



2. That before the hatching of the Phyllosoma larva certain extremities or parts 

 of extremities degenerate, to appear anew on the older Phyllosoma larva ; this 



