Introductio7i to Animal Morphology. 2 1 3 



capillaries on the intestine. The blood may be color- 

 less, with colored corpuscles (Glyceria, Phoronis, 

 Dujardiniae), or more commonly is a yellow, green, 

 red, or blue serum with colorless corpuscles. The 

 color is often dissimilar in allied species. 



Respiration may take place by the surface, by the 

 water admitted into the perivisceral cavity, or by gills 

 which may be modified, filiform cirri, over or under 

 the parapodia, or dermal, ciliated, comb-like, pinnate 

 or branched processes, into which often pouches of 

 the body cavity enter, attached to the notopodia. In 

 the tube-dwellers there are long contractile threads in 

 bundles, or spirals, or fans, or tree-like, with a carti- 

 laginous axis of support (Sabella). Some of these 

 cirri may lose their respiratory functions, become 

 club-like, and act as opercula to the tube. This 

 operculum may have a calcareous, terminal disc 

 (Serpula), or it may be dilated into a brood-pouch for 

 the young (Spirorbis). In Fabricia, a temporary tube- 

 dweller, the operculum retrogrades into a simple 

 tentacle. The gills contain either simple ceecal diverti- 

 cula from the transverse communicating vessels, or 

 they may have separate inferent and efferent vessels. 

 Colobranchus has eight oval, ciliated (respiratory r) 

 laminae around the anus, and the lower end of the in- 

 testine is also ciliated. In Hesione, air bubbles have 

 been seen emitted both by the mouth and anus. In 

 some Syllidae the periodic taking in and expulsion of 

 water from the intestine has been noticed. 



Each metamere has usually a pair of symme- 

 trical excretory [segmental) organs, often acting as 

 ducts for the sex-glands. These may be simple 

 mucous pouches in Tubifex, Nais, &c., larger and 



