256 A MONOGRAPH OF THE AUSTRALIAN APHRODITEA, 



function in connection with respiration. In these genera the 

 dorsal surface is covered with a coating of felted hairs which 

 stretch across from one side to the other, and enclose a canal 

 open in front and behind, and having for its floor the dorsal wall 

 of the body with the elytra and the ** branchial" tubercles 

 These authors regard the oxygenation of the perivisceral fluid as 

 taking place through the thin integument covering the scale- 

 tubercles and the tubercles at the bases of the dorsal cirri, and 

 have observed the scales to be subject to rythmical movements 

 by means of which a current of water is driven constantly over 

 the dorsal surface, thus renewing the water in contact with the 

 ** branchiae." In species in which the felt-like dorsal covering 

 does not exist, this function would appear to be in abeyance ; and 

 in Polynoe and allied genera, so far as I have observed, the elytra 

 remain perfectly motionless while the animal as a whole is at 

 rest. 



When the ripe ova are discharged from the orifices of the 

 segmental organs, they are carried by ciliary action towards the 

 under surface of the elytra, where they remain, adhering by means 

 of a viscid secretion, until they are tolerably well advanced. 

 Impregnation probably takes place while the eggs are in this 

 situation ; and I have found still crowding in great masses under 

 the scales, free embryos which had reached the cephalotrochous 

 stage first described by Sars.^' 



Segmental Organs and Sexual Glands. 



The position and relations of these organs have been entirely 

 misunderstood both by WiUiams and Ehlers, and I find their 

 statements repeated in the latest work on general zoology,! so 

 that, though unable to obtain here all the literature of the subject, 

 I am justified in concluding that these errors have not yet been 

 corrected and explained. 



* Archiv. fiir Naturg., 1845. 

 t *' Pagenstecheij Allgemeine Zoologie, Band iv." 



