ANATOMY AND CLASSIFICATION OF THE ARBNICOLID^. 545 



green molecules are either excretory products of the walls of 

 the nephridia or else chlorogogenous cells which have been 

 swept into the nephridia. Further^ the description and 

 plates show that the gonads are developed in connection with 

 the funnels. 



From the rest of this interesting account of Scalibregma 

 it appears that there is a single dorsal " heart " which drives 

 the blood forward to the gills like a Terebellid, and unlike 

 Arenicola. There are two oesophageal pouches, Bixt more 

 distinctive than even these is the definitely ganglionated 

 ventral nerve- cord. These characters^ taken in connection 

 with the far more complex parapodia which form swimming 

 plates, the absence of crotchets, and the arrangement of the 

 gills, seem to show that the Scalibregmidge have a resem- 

 blance to the Arenicolidse merely in the general arrange- 

 ment of the coelom, in the digestive system, in the form of 

 the nephridia, and structure of gonads ; but that in all other 

 respects — in external features, in the vascular and nervous 

 systems — the two families are widely different. In fact, it 

 seems more likely that the Scalibregmidae are aberrant Tere- 

 bellids. 



The accounts of the vascular, nephridial, and reproductive 

 systems of the Opheliidae are so fragmentary as to preclude 

 any general comparisons with these organs in Arenicola. 

 Rathke's (1843) excellent descriptions of their anatomy are 

 still the only accounts of the geiiera Ammo trypans and 

 Ophelia that can be considered at all complete, but naturally 

 some of his statements, e. g. that besides the opening of the 

 nephridium there are in Am mo try pane oestroides (now 

 called Ophelia acuminata) ovipores and openiugs into the 

 coelom, require corroboration ; which, however, has not been 

 attempted. Thirteen pairs of nephridiopores are described 

 in this species, six in Ophelia limacina, and the drawing 

 of a nephridium of the former might stand for that of 

 Arenicola. The large funnel, the nephrostomial vessel, the 

 oblique muscles, are all exactly given in Rathke's figure of 

 Ophelia, as they lie in a specimen of a lugworm. Further 



