204 



CRUSTACEA. 



appendages, which however are devoid of the special masticatory- 

 hook found in the Branchiopodan NaujMiis. 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 the body the rudiments of six pairs of limbs 

 {p^-p^') are visible in the form of transverse swellings. In the 



cephalic region, 

 the ISTauplius 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 



Fig. 97.— A^awpZiiis stage of imjie^is 6mc/i2/«ra (after Grube). a", and of the body- 

 secoiid antenna; A:, masticatory process of the same; md, , ,-, 



mamiibie. 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 ]S^auplius eye persists in the generation 

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

 developing from summer eggs. 



The genus Lepdodora, 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. 



Fio. 98. — Metananplius stage of Lejitodora hyalina developed from a 

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

 mandible ; pi-pVi, rudiments of the first six pairs of thoracic 

 limbs ; ol, upper lip. 



The sumiii el- 

 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 Bythotrcphcs and 

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



