152 ZOOLOGY 
ventral half; the notopodiwm and the newropodium respectively. 
Each of these may bear (i.) a bundle of bristles, the setae ; 
(i1.) in the midst of the setae, a single large bristle, the 
aciculum; (iii.) solid fleshy prolongations of the body-wall, 
containing a nerve, and probably tactile in function, the cirrhi; 
(iv.) respiratory organs, processes of the body-wall well sup- 
plied with blood-vessels, and sometimes containing a prolonga- 
tion of the body-cavity, the branchiae. These last are borne 
as a rule only by the notopodium. 
The parapodia are not well developed in Avenicola. The 
first nineteen segments bear each a small notopodium in 
which a bundle of setae spring, and on the ventral surface a 
small neuropodium, which bears a row of hooked bristles. 
The gills borne on the 7th to the 19th segments are 
feathery branched structures, through whose thin walls the red 
blood is visible. The tail bears no parapodia. 
Each of the segments of the body is divided into five small 
rings: an unusual feature in Chaetopods, recalling the annula- 
tion of the HIRUDINEA. 
The integument consists of the same elements as are 
found in Lumbricus: (1.) a cuticle, (i1.) an epidermis of columnar 
cells crowded with pigment cells, (i11.) a continuous sheath of 
circular muscles, (iv.) a layer of longitudinal muscles, much 
broken up by the presence of the bundles of setae, etc., and 
(v.) a lining of peritoneal epithelium. 
The coelom is very spacious; at the anterior end of the 
body it is traversed by three septa, which mark the limits of 
the first three segments. There are no other septa in the first 
nineteen segments, but the tail is divided into as many 
chambers as there are rings by vertical septa. The body is 
further partially divided into three divisions by two longi- 
tudinal incomplete mesenteries, which run obliquely from the 
side of the body to near the middle ventral line. The central 
division lodges the alimentary canal, the lateral contain the 
nephridia. This dividing up of the body-cavity recalls the 
arrangement in the Archiannelids. The coelom is full of a 
corpusculated fluid, in which, during the breeding season, the 
ova and spermatozoa are found in great quantities. 
The alimentary canal runs in a straight line from the 
