56 SUPPLEMENT ,. 



designated by the name of lobules, mammillary, cirrhous, or 

 squamous, according to their form. 



The nipples, or maimnilloi, are elongations, more or less 

 considerable, of the sides of the segment, at the extremity of 

 which the setae are implanted. Sometimes they are almost 

 nothing, and then the articulations of the body are very little 

 sensible ; at other times, on the contrary, they are excessively 

 long, and then the body appears deeply incised throughout 

 its entire length. It is those which support the lobules, of 

 which we have been just speaking. 



The setcB (whose structure we will give more in detail by 

 and by), are stiff, hard, fragile parts, which are implanted 

 more or less deeply into the skin of the chetopoda, and, in 

 general, are considerably numerous. There is but a single one 

 in some na'ides. They form simple or divided fasciculi, placed 

 at the extremity of the nipple, and between the two cirri of 

 the appendage. 



Modern naturalists, such as M. de Blainville, Otho Fabri- 

 cius, and Savigny, distinguish three kinds of setae. 



1 . The simple setae, which are slender, pointed, and straight 

 at their extremity ; these are the most common, and such as 

 fasciculate the best. 



2. Hooked setae, which are still rather slender, and curved, 

 and terminated by a hook at their extremity. 



3. The needles, or spines (aculei), which are straight, like 

 the simple setae, but which are always thicker, and much 

 stiffer ; such are to be found in some of the aphroditae. 



We have now stated all which can enter into the composi- 

 tion of the most complex appendage of a chetopoda. 



When it is not divided into two parts, one superior and the 

 other inferior to the lateral line, the appendage is composed 

 of a single oar. In the other case, it is in the form of two 

 oars. 



