The last six pairs belong to the abdomen and are primarily swimming- 

 paddles, some of which, in the male, are modified to subserve reproduction, 

 and in the female subserve nutrication or the care of the developing embryo. 



Just as the abdomen furnishes the type of the unmodified Crustacean seg- 

 ment, so also it gives us the type of the Crustacean appendage. 



An appendage taken from, say, the 3rd abdominal somite consists of a 

 stalk, or protopodite, to the end of which two leaf -like branches are articulated, 

 the inner branch being known as the endopodite the outer as the exopodite. The 

 stalk itself consists of two segments, a short basal piece or coxopodite, by means 

 of which it is articulated to the somite, followed by a larger sub-cylindrical 

 hasipodite'. 



Although a minority of the appendages of a Decapod Crustacean exactly con- 

 form to this description, yet they all can be referred to this general plan, or type. 



3. Of the Segments and Appendages of the Head. 



The first segment, or ophthalmic somite, is hidden by its appendages, the 

 eyes. If the eyes are pushed aside, we shall find, between and just below 

 them, a small plate of leathery consistence : this is the sternum of the ophthal- 

 mic somite, and is all that we can with safety recognize as belonging to that 

 somite. Its appendages, the eyestaJks, each consist of a simple two-jointed pro- 

 topodite, the large compound facetted eye terminating and forming the chief 

 part of the second joint. 



The second segment, or antenmdar somite, is also a good deal hidden. All 

 that we can recognize as certainly belonging to it is its sternum, which is a 

 narrow partition between the antennules ; but the " orbits," or facets on either 

 side of the carapace on which the eyes rest, are very probably its epimera. Its 

 appendages are the antennules, each of which consists of a thickish stem or 

 peduncle (protopodite) to the end of which two long slender t&:^eYmg flagella 

 (exopodite and endopodite) are articulated. The protopodite is abnormal in 

 consisting of three segments : the proximal segment contains the avditori/ sac, 

 the small orifice of which is seen at the inner border of the upper surface of 

 the segment, in its posterior half. The flagella consist of a series of little rings 

 with fine setae : the outer, or olfactory flagellum, is the thicker of the two, and 

 its setae are larger and more thick-set, especially in its distal part. 



The third segment is the antennal somite and its appendages are the antennse. 

 The broad space between the bases of the antennte, known as the epistome, is the 

 sternum of this somite, behind the outer ends of which the epimera are visible. 

 The pleura and the tergum of this somite probably form all that part of the 

 carapace that lies in front of the cervical groove. 



