294 



CRUSTACEA. 



being short and unjointed, while the outer flagellum, beset at its 

 end with olfactory filaments, has broken up into short rings. The 

 second antenna (Fig. 137 B) has the rudiment of the flagellum 

 (endopodite) greatly developed ; but the softer portions have with- 

 drawn from the spinous process and the exopodite as a sign that 

 these appendages will be lost in the next moult. On the mandible 

 ((7), a finger-shaped and still unjointed mandibular palp has developed. 

 The two maxillae (D and E) have undergone changes which are 

 comparatively slight, while in the two anterior maxillipedes the 

 exopodites are divided up at their ends into short joints, and seem 



beset with numerous 

 swimming setae. The 

 rudiments of the third 

 pair of maxillipedes 

 and of the five ambulatory limbs 

 (Fig. 138, IV- VIII) are already 

 conspicuous. They, however, have 

 no clothing of setae and are still 

 functionless, being carried closely 

 pressed against the sternal surface 

 of the body. These rudiments 

 develop gradually, but always in 

 the direction of the form of the 

 adult appendages. The third max- 

 illipede thus soon shows all the 

 parts of the future limb, a two- 

 jointed exopodite and the branchial 

 appendages, which also develop on 

 the three following pairs of limbs. 

 The most anterior pair of ambu- 

 latory limbs with their pincers 

 develop greatly. On the abdomen, 

 the pleopoda have now developed 

 as indistinctly two-jointed append- 

 ages, while the sixth pair are still simple stumps. An exopodite 

 does not develop on the'ambulatory limbs. The My sis stage is thus 

 suppressed in the metamorphosis of the Brachyura, and is repla 

 l>!l the Metazoaea stage. This is an interesting case of simplification 

 of the course of development. 



The Metazoaea passes into the young form of the Brachyuran 

 known as the Megalopa (Fig. 139 A and B), which brings about the 



Fio. ISS.—Zoaea of Maja after ecdysis 

 (after Claus, from Lang's Text-book). 

 1, 2, first and second antennae ; I, II, III, 

 first three maxillipedes; IV-VIII, first 

 five ambulatory limbs; a„-a G , last five 

 pleopoda ; h, heart. 



