222 
BULLETIN OF THE BUREAU OF 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 
limbs 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 
Tabes 4. — The Body Segments and Appendages of the Lobster 
Divisions of body. 
No. of 
somite. 
Name of somite. 
Name of appendage. 
Functions of appendage. 
ii 
First antennal 
Antennule 
Olfactory cr chemical, chiefly through 
outer branch, and static. 
Head (6) 
hi 
Second antennal 
Antenna 
Tactile chiefly, and probably chemical 
IV 
Mandibular 
Mandible 
Crushing and triturating small, hard parts 
of food. 
V 
First maxillary 
First maxilla 
Masticatory and chemical, but chiefly for 
passing the food. 
VI 
Second maxillary 
Second maxilla 
Respiratory chiefly; also chemical, masti- 
catory, and for passing on the food. 
' VII 
First thoracic 
First maxilliped 
For passing, and like the maxillae possibly 
subserving the chemical sense. 
VIII 
Second thoracic 
Second maxilliped .... 
For transference of food, the chemical sense, 
and respiration. 
IX 
Third thoracic 
Third maxilliped 
Chiefly masticatory, with brushes for clean- 
ing. 
Thorax (8) 
X 
Fourth thoracic 
Great cheliped, or first 
pereiopod. 
Chelate; big claws adapted on one side for 
crushing and on other for seizing and 
rending prey; respiratory, tactile, and 
possibly olfactory. 
XI 
Fifth thoracic 
Second pereiopod 
Chelate; ambulatory, tactile, and possibly 
with chemical sense, for seizing, testing, 
and transference of food; respiratory. 
XIII 
Seventh thoracic 
Fourth pereiopod 
Nonchelate; the same 
XIV 
Eighth thoracic 
Fifth pereiopod 
Non chelate; the same, and for cleaning 
swimmerets. 
