CHAETOPODA 143 
groove of Protodrilus has in this genus closed in, and forms a 
canal within the nerve cord. ed blood occurs in this genus, 
and the dorsal vessel gives off lateral branches, which, however, 
end caecally. The sexes are distinct, and the ovaries or testes 
arise in the posterior segments (Fig. 90). 
The last member of the group, Dinophilus, is a minute 
marine animal. ‘Two species, J). gigas and D, taeniatus, have 
recently been described by Weldon and Harmer from the coast 
of Devonshire and Cornwall. The body consists of a head or 
prostomium, which bears two eye-spots, and whose cilia are 
uniform or arranged in two preoral circlets. The mouth opens 
on the second segment or peristomium, and then follow five 
or six segments, and finally a postanal unsegmented tail. In 
both the above-mentioned specimens the entire ventral surface 
of the animal is uniformly ciliated, and each segment has one 
or two bands of cilia. WD. vorticoides is uniformly ciliated all 
over. The nervous system is in contact with the skin. The 
coelom is traversed by strands of connective tissue in D. gigas ; 
and in D. taeniatus there are more definite spaces connected 
with the inner ends of the nephridia. In D. gigas an excretory 
system of the Platyhelminthine type, with flame cells, has 
been described, but in D. taeniatus and D. gyrociliatus, 5 pairs 
of nephridia are found, each with a triangular appendage 
hanging into the lumen of their ciliated duct. The sexes are 
separate, and in the male YD. taeniatus the fifth pair of 
nephridia appear to have become modified and form vesiculae 
seminales. A penis is present, and seems to be inserted 
indifferently into any part of the skin of the female. 
There is little doubt that Dinophilus should be classified 
with the other members of the group Archiannelids; on the 
other hand, its median genital pore, the presence in some 
species of the Platyhelminthine excretory system, and the 
method of fertilisation adopted by PD. taeniatus which is 
paralleled in the Polycladida, support the view of the Platy- 
helminthine origin of these worms. 
THE OLIGOCHAETA. 
CHARACTERISTICS.— The Oligochaeta are characterised by the ab- 
sence of antennae, parapodia, branchiae, and cirrhi. Their 
