AFFINITIES OF ECHIUKUS UNICINCTUS. 89 



werdeu, Kiemen im vollen Siuno der Wortes, volliiv den aualoi? soa^enannten ' Wasser- 

 lungen ' der Rolotlminen.'" Sclimarda's * opinion coincides with this, and Forbes and 

 Goodsir'sf went the length of calling the anal vesicles " Atheinsacke." 



There may be rectal respiration, but it is extremely doubtful if the anal vesicles act 

 as lungs, for though there be a current of water in and out of the anus, it cannot 

 possibly flow freely through the vesicles, their structure rendering this impossible. In 

 the first place, the apertures leading into the vesicles from the rectum are too small to 

 allow of any appreciable amount of water entering them ; but allowing that the water 

 does penetrate to the vesicles, it cannot get further, for the ends of the ciliated canals 

 (described minutely by Spengel in IJc/ii/inm 'Fallasii) Avould act as valves, completely 

 preventing the jmssage of any liquid into the body-cavity; lastly, the cilia in the canals 

 are directed inwards, as Spengel and Greeff both remark, which is conclusive evidence 

 tbat fluid may be carried from the body out at the anus but not in the opposite 

 direction. 



It, therefore, appears probable that the function of these organs is excretory ; the 

 granule-containing cells in the walls of the vesicles may function as carriers which 

 collect w'aste matter, and throw it and themselves away. The vesicles are full of bodv- 

 cavity fluid, which may be the product of the ordinary cells forming the peritoneal 

 lining of the ccelom ; for in no part of the animal is there any glandular tissue like the 

 chloragogenous tissue in Lumbricus Avhich secretes the coelomic fluid in that worm. It 

 has been suggested that the anal vesicles secrete the coelomic liquid, though, so far as I 

 can judge from my observations in Echiuriis umciuctun, tliere is no evidence to support 

 such a view. 



Segmental Organs. — Posterior to the two anterior ventral setae are two pairs of 

 nephridia, or segmental organs (PL 7. flgs. 5, 12, o.s.), opening on the one hand into the 

 body-cavity, and on the other to the exterior. The lips of the inner opening are 

 produced out right and left into long tapering arms (PI. 7. fig. 12, l.s.), which are spirally 

 grooved and densely ciliated, but w^hich contain no canal. Drasche says there are 20-30 

 coils in each s])iral arm ; but in taking the average among many of my specimens, I 

 find it is less than this, there being not more than 12-20 coils. At the base of these 

 arms, and exactly between them, is the aperture leading into the vesicle from the body- 

 cavity (PI. 9. fig. 25 ; PI. 10. fig. 38, ap:-) ; the contents of the vesicle are discharged 

 externally through a minute pore in the body-wall {(ip.^). PI. 9. fig. 25 represents a 

 section through the entire body of the worm, and in it are seen the two openings of the 

 vesicle {up}, ap.-), the spiral arms {l.s.), and the vesicles containing ova. 



In some individuals the vesicles, being highly muscular, an^ enormously distended by 

 the mass of reproductive products contained in them ; they stretch back some way 

 among tlie coils of the alimentary canal, when they are in this inflated condition — 

 this is also the case in Bonellia (Greeff). 



Each vesicle possesses but one chamber, whereas in Bonellia it is divided into two by 



* Zur Naturgcsch. tier Adria : 1. Bonellia viridis, pis. 4-7, in Memoirs of the Acad, of Vienna, 1852, vol. ii. 

 + "On the Naturiil History and Anatomy of Thahisseiini and Echiurus" Edin. Now Phil. Journ. 1841, vol. xxx. 

 j)l. vii. 



