422 Edwin s. goodrIcb. 



vascular system. To these characters Fraipont added the 

 simple primitive structure of the nephridia running in the 

 body-wall^ below the ccslomic epithelium. 



That the general organisation of Polygcrdius and Proto- 

 drilus is simple cannot be denied; but that -his simplicity is 

 necessarily of an archaic nature remains to be proved. To a 

 great extent it may be due to a general tendency Lc simplifi- 

 cation shown in the smaller representatives of many families 

 of Polychaetes, especially amongst sand-inhabiting forms. 

 It is well known that in the smaller Syllids, Opheliids, 

 Eunicids, etc., the nerve-cords are closely connected with the 

 epidermis. The intimacy of the connection between the 

 epidermis and the nerve-cords in the Polygordiidse appears 

 to me to have been a little exaggerated by Fraipont (2). 

 Protodrilus I have not studied ; but in Polygordius the dis- 

 tinction between the two does not seem to me to be mucli 

 less marked than in many small Polychaetes (in Saccocirrus a 

 line of demarcation can always be made out separating the 

 nerve-cord from the epidermal cells). However, the absence 

 of ganglionic concentrations may certainly be archaic ; but 

 the presence of ganglia in such forms as Dinophilus and 

 Histriodrilus, animals considered by some authors to be 

 allied to the Polygordiidee, tends to show that it is a cha- 

 racter of no very fundamental importance. 



Again, with regard to the absence of cii'cular muscles ; not 

 only have they been expressly stated to exist in Polygor- 

 dius Villoti by Perrier (11), but surely if we consider how 

 well developed they are in Nemertines and Platyhelminths, 

 the assumption that their absence is primary and not secon- 

 dary does not seem to be justified. The peculiar develop- 

 ment of the oblique muscles in the Polygordiidas is much 

 more like what we find in many Polychseta where the para- 

 podia are reduced (Arenicola, Capitellidse, Opheliidse, etc.), 

 than anything we know of in the lower classes of Coelo- 

 mata. 



Moreover little importance can be attached to the position 

 of the nephridia ; in almost all Polychseta these organs are 



