ix EXCRETORY SYSTEM OF NEREIS 253 



is a highly complex form of excretory material, more complex 

 than guanin, for instance, which exists in the corpuscles of the 

 Capitelliformia. 



In Glyceridae, Capitelliformia, and Polycirrus haematodes (a 

 Terebellid), the vascular system is absent, and the coelomic 

 corpuscles become coloured by haemoglobin, and in order that 

 the coelomic fluid may be distributed to the organs of the body, 

 the peritoneum is ciliated along certain definite tracts. The fluid 

 in these " anangian " worms thus combines originally separate 

 functions, and behaves like the " blood " of Vertebrates. 



The excretory system is represented by a pair of nephridia 

 in each segment, with the exception of a few anteriorly and a 

 few posteriorly. The 

 nephridium of Nereis 

 diners from that of 

 most other Poly- 

 chaetes hitherto ex- 

 amined carefully, 

 and rather resem- FlQ 12g ._ Nephridium of Ntnigm (Frora _ 



lues that of the Funnel ; n, neck, which passes through a septum ; t, 



Oligochaetous En- coiled tubule ; C) connective tiasue > <*> duct - 

 chytraeids. It consists of a compact gland-like organ, containing 

 a much coiled tube, ciliated for the greater part of its length, but 

 deprived of cilia in its last coils ; this latter part or duct 

 leaves the "gland" and pierces the body- wall, opening to the 

 exterior at the base of the parapodiuin. The ciliated canal 

 passes forwards into the next segment, where it opens by a 

 funnel into the coelom. The lip of the funnel is extremely 

 curious, for the cells constituting it are drawn out into very 

 long, delicate processes covered with cilia. 1 



In most Polychaetes the nephridium is a wide, sac-like tube 

 as in Arenicola* (Fig. 129). Its walls are covered by a dense 

 network of blood-vessels, and it not only acts as an excretory 

 organ, but also as a genital duct (see p. 273). 



Excretion, in the strict sense of the word, is carried out by 



1 Goodrich, Quart. J. Micr. Sci. xxxiv. 1893, p. 387. 



2 Benham, Quart. J. Micr. Sci. xxxii. 1891, p. 325. See also Bourne (nephridium 

 of Polynoe), Tr. Linn. Soc. (Zool.), ii. 1883, p. 357 ; Meyer, for nephridium of 

 Terebellidae, Sabellidae, and Cirratulidae, in Mt. Zool. Slot. Ncapel, vii. 1887, p. 

 592. 



