204 



CRUSTACEA. 



-/-w 



FIG. W.Nauplius stage of Limnetis Iracliyura (after GRUBE). a", 

 second antenna ; k, masticatory process of the same ; md, 

 mandible. 



appendages, which however are devoid of the special masticatory 

 hook found in the Branchiopodan Nauplius. The mandibles (md)- 

 consist of the basal blade and a long unjointed oar-shaped palp. 

 The oral aperture is overhung by a large upper lip (ol). In the 

 thoracic section of tile body the rudiments of six pairs of limbs 

 (p r -p vi ) are visible in the form of transverse swellings. In the 



cephalic region, 

 the Nauplius eye 

 alone is recog- 

 nisable, the com- 

 pound eyes de- 

 veloping at a 

 later stage. Fur- 

 ther metamor- 

 phosis takes place 

 by the develop- 

 ment of the limbs 

 and of the body- 

 segments, the 

 growth of the 



dorsal shield, the diminution of the upper lip, the degeneration of 

 the mandibular palp, and the acquisition of the characteristic 

 curvature of the body. The Nauplius eye persists in the generation 

 coming from the winter egg, whereas it is wanting in individuals 

 developing from summer eggs. 



The genus Leptodora, in the metamorphosis of the winter eggs- 

 and in the 

 Branchiopoda- 

 like Metanau- 

 plius stage, as 

 well as in many 

 other respects, 

 has thus re- 

 tained primi- 

 tive characters 

 among the 

 Cladocera. 



The summer 

 and winter eggs 



differ not only with regard to the development of the embryo, but in other 

 points as well. It has already been indicated (p. 114) that, in Bythotreplies and 

 Leptodora, the type of cleavage of the summer egg differs from that of the winter 



Fio. 98. Metanauplius stage of Leptodora hyalina developed from a 

 winter egg (after G. O. SARS). ,', first, a", second antenna; md, 

 mandible; pl-pVl, rudiments of the first six pairs of thoracic 

 limbs ; ol, upper lip. 



