LOBSTER OH CEATFI8H 149 



Compare the antennule with the antenna. How does 

 the protopodite of the former differ from that the of 

 latter? On the basal joint look for the opening of the 

 auditory organ. Note the distribution of setae. Ex- 

 amine the two feelers. Which segment do they repre- 

 sent ? Compare with the large one. Draw. 



The most anterior of the cephalic appendages (?) is 

 the eye-stalk or ophthalmite. "What segments can 

 you find in it ? Draw. 



Go over all of the appendages again. Can you make 

 out that they are all constructed upon the same funda- 

 mental plan, *'. e., that the appendages are homologous ? 

 What would you consider to be the structure of a typical 

 appendage ? Divide the appendages into such groups 

 as you think their structure warrants. How many 

 groups do you make? Do the groups gradually shade 

 into one another structurally? In each group, what 

 is the most important modification of the typical seg- 

 ment? If the morphological rule that each pair of 

 appendages corresponds to a segment be correct, how 

 many segments are there in the body of the animal ? 

 How many are plainly visible ? How many are " con- 

 solidated"? In what regions are they most plainly 

 seen ? How many are there in each region ? In which 

 region is consolidation carried to the greatest extent ? 

 Note the abrupt bend, the cephalic flexure, which is 

 made by that part of the body anterior to the mouth. 

 As regards segmentation of the bodj'- and appendages, 

 how do the lobster and crayfish compare with the earth- 

 worm ? How as regards cephalization, i. e., the ten- 

 dency to consolidate the mouth parts, eyes, ears, brain, 

 etc., into a distinct head-region ? 



D. The gill-chamber. — Between what parts of the 



