222 



BULLETIN OF THE BUREAU OP FISHERIES. 



APPENDAGES. 



The 20 pairs of appendages of the lobster are developed as tubular folds or out- 

 growths of the body wall, and consist of ectoderm with mesodermic cores, a rule which 

 seems to be broken only in the case of regenerating limbs, where ectoderm appears to 

 contribute to the renewal of both muscles and nerves. The order of embryonic develop- 

 ment is: (i) Antennules, (2) mandibles, (3) antennae, (4) maxillae and the thoracic 

 Umbs in regular succession. Four pairs of swimmerets (somites xvi-xix) are released 

 together in the second larval stage (fig. 41); the uropods in the third stage (fig. 42) 

 and the first pair of pleopods, which are the last to appear, are not usually recognizable 

 until the sixth molt or later. 



The eyestalks, which are omitted from the enumeration given above, and the 

 antennules are prostomial in origin, while the originally postoral antennae reach a 

 position in front of the mouth by the twentieth day, when the compound eyes are dis- 

 tinctly lobate. Segmentation in the limbs is a gradual process, constrictions early 

 marking future joints, while the division into outer and inner branches begins at the 

 apex of the appendage except in the antennules, as noted below. Most parts of the 

 adult appendages are recognizable in the first larva, and all, excepting those of the xv 

 somite, in the lobsterling. From the fourth stage on through the adolescent period 

 the changes are gradual and relatively slight, excepting only those which involve the 



Table 4. — The Body Segments and Appendages op the Lobster 



