A CRAYFISH OR A LOBSTER 35 
No. oF SOMITE. NAME OF APPENDAGE. PROT. Ex. Enp. 
Head... 
aorWwWnN re 
1st maxilliped + + + 
Thorax... 
Abdomen . j 17 
Write opposite the number of each somite, in your notebook, 
first, the name of the appendage belonging to it, then indicate 
what parts that appendage possesses by a “+” and what parts 
it lacks by a “—” under the appropriate head, as is shown 
above in the case of the sixth somite. 
The gills. Remove the left-hand branchiostegite. Place the 
animal in water and study the gills on the left side. These 
organs may occur on the eight thoracic somites, and on each 
segment they may be attached either to the basal joint of the 
leg, when they are called podobranchiz, to the flexible joint by 
which the leg articulates with the body, when they are called 
arthrobranchie, or to the body-wall just above the leg, when they 
are called pleurobranchie. A single thoracic somite may bear 
on each side four gills, —a pleurobranch, two arthrobranchs, 
