1889. ] NATURAL HISTORY OF DERO. 441 
a complete list of literature referring to this genus, for the reason 
that Bousfield has gone into the matter somewhat fully. 
Concurrently with the development of the sexual organs, certain 
of the lower aquatic Oligocheta have been stated to show other 
peculiarities, so that there is a kind of dimorphism among the 
individuals. The sexual individuals of Dero, in common with other 
Oligochzeta, show no traces of multiplication by budding ; connected 
with this is a regularity in the arrangement of the seta-bundles at the 
Fig. 1. 
Ventral aspect of sexually mature Dero. 
cp., spermathecal pores; ¢, male pores. 
distal extremity of the body. In the asexual form, on the contrary, 
the continual growth of the posterior groups of sets appears to 
produce an irregularity in the disposition of the seta-bundles ; the 
termination of these, for example, in D. perrieri (Bousfield) (see 
Proc, Zoo. Soc.—1889, No. XXX. 30 
