288 LIONEL JAMES PICTON. 



A very striking fact has been noticed by Bles in Siphono- 

 stoma, which, so far as I have seen, holds good in other 

 Chlorhsemidae : the great single anterior pair of nephridia is 

 totally deprived of blood-vessels. Their near proximity to the 

 heart-body, the occurrence of the similar granules in both, and 

 in the coeloraic corpuscles, coupled with this singular fact, are 

 very strong arguments in favour of the way of excretion of 

 waste blood-substances proposed. On the other hand, pigment 

 lymph-glands similar to those mentioned by Ed. Meyer in Capi- 

 tellidee and Terebellidae are described by Haswell in the gills 

 of Stylaroides cinctus, accompanying the branchial vessels, 

 and containing a reddish-brown pigment ; and these oflFer an 

 alternative possibility as a way of excretion from the blood. 



Terebellidae. 

 The arrangement of the blood-vessel is similar to that in the 

 Chlorhsemidse, and the branchial heart, formed by the union 

 above the gut of a pair of peri-intestinal sinuses, runs forward 

 freely suspended in the body-cavity by a dorsal mesentery, and 

 ends, after piercing the dissepiment, by dividing into two 

 branches which carry blood to the three pairs of gills (fig. 3). 

 In some species a small median vessel proceeds forwards from 

 the point of division ; but in Polymnia this is represented by a 

 median vessel which springs from the base of the heart-body, 

 and runs forward between that and the gullet.^ Thus in 

 Polymnia all the blood which flows over the heart-body goes to 

 the gills. The heart-body itself is in the form of a cylindrical 

 rod, extending from the posterior end of the heart to a point a 

 short distance beyond the dissepiment. It is attached to the 

 heart wall by fine processes, both at its extremities and some- 

 times at other points. Amongst the many Polymnia which I 

 examined, a single specimen showed a peculiar abnormality of 

 the organ. Instead oi ending at the posterior extremity of the 



resemblance to bodies described by Metcbnikoff in the spleen of the Jerboa 

 (22, pi. iii). In that case the figure-of-eight shaped bodies represent reactions 

 against bacteria. 



' Milne-Edwards' otherwise excellent description of the blood-system is 

 wrong on this point ('Ann. Sol, Nat.,' 2e ser., t. x, p. 199). 



