294 



CRUSTACEA. 



being short and unjointetl, while the outer flagelhini, 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 

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

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

 comparatively slight, Avhile in the two anterior maxillipedes the 

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



lieset Avith numerous 

 swimminj^- setae. The 

 ^^^^"^^^^ rudiments of the third 

 l)air 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 tiieir 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. I'/ie Mysis stage is tints 

 suppressed in the metumoiphosis of the Brachyura, and is replaceil 

 hy the Metazoaea stage. This is an interesting case of simplification 

 of the course of develojiment. 



The Metazoaea passes into the young form of the Brachyuran 

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



Vv'.. 138. — ZooMt of Maja after ecdysis 

 (after Glaus, fi'Qiii Lang's Texl-liook). 

 1, 2, first and .second antennae ; 7, //, 7//, 

 first three maxiUipedea ; IV-VIIf, first 

 live ambulatory limbs ; (i.j-Ug, last five 

 pleopoda ; /;, Lenit. 



