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LIBBIE H. HYMAN 



genus Dero is enlarged to form a gill pavilion, remains alive 

 longer than any other part of the body. The anal segment is, 

 of course, one of the oldest parts of the body in Annelids, but in 

 forms which divide by fission, each anterior zooid has to form a 

 new anal segment, while the posterior zooid retains the old anal 



i 



Fig. 8 Three stages in the disintegration of Dero limosa. 



segment. It thus happens that in any individual Dero, the 

 anal segment may be very old, or it may be relatively young, 

 and this accounts for differences in the time of disintegration 

 of this part as compared with the rest of the body. 



The axial gradient of Dero is modified by the presence of zooids. 

 When the worms have reached a length of 10-15 mm. with 50-80 



