VII THE STUDY OF ZOOLOGY 201 



and yet different from, the others. The ring is 

 essentially the same as in the other divisions ; but 

 the appendages look at first as if they were very 

 different ; and yet when we regard them closely, 

 what do we find ? A stalk and two terminal 

 divisions, exactly as in the others, but the stalk is 

 very short and very thick, the terminal divisions 

 are very broad and flat, and one of them is divided 

 into two pieces. 



I may say, therefore, that the sixth segment is 

 like the others in plan, but that it is modified in 

 its details. 



The first segment is like the others, so far as its 

 ring is concerned, and though its appendages differ 

 from any of those yet examined in the simplicity 

 of their structure, parts corresponding with the 

 stem and one of the divisions of the appendages 

 of the other segments can be readily discerned in 

 them. 



Thus it appears that the lobster's tail is com- 

 posed of a series of segments which are funda- 

 mentally similar, though each presents peculiar 

 modifications of the plan common to all. But 

 when I turn to the forepart of the body I see, at 

 first, nothing but a great shield-like shell, called 

 technically the " carapace," ending in front in a 

 sharp spine, on either side of which are the curious 

 compound eyes, set upon the ends of stout movable 

 stalks. Behind these, on the under side of the 

 body, are two pairs of long feelers, or antenna?, 



