426 EDWIN S. GOODRICH. 



This group, containing the genera Polygordius, Protodri- 

 luSj and Saccocirrus, to which Lankester's name Haplodrili 

 might still be applied, we should regard not as ancestral to 

 all the Annelida, but as composed of specialised offshoots of 

 the Annelid stem (probably, indeed, of the Polychgete stem 

 itself), in some respects primitive, in other respects highly 

 specialised.^ As specialised characters we may reckon the 

 development of a contractile " head cavity " (Protodrilus and 

 Saccocirrus), of a very complex genital apparatus (Saccocir- 

 rus), and the partial (Saccocirrus) or total loss of parapodia 

 and chsetse (Polygordius and Protodrilus). All three genera 

 possess two prostomial tentacles. 



If it be objected that in the foregoing pages I have 

 tacked much theoretical speculation on to very little fact, my 

 excuse must be that I have endeavoured not so much to add 

 to the number of existing theories as to diminish it, and so to 

 bring back the question of the affinities of Polygordius and 

 Saccocirrus to the position it occupied before the " Archi- 

 annelid theory" was put forth. 



The remarkably close affinity which has been shown to 

 exist between Saccocirrus and Protodrilus seems to force on 

 us the conclusion that the absence of parapodia and chaetse in 

 the Polygordiidge is not primitive, but secondary. 



List of References. 



1. BoBUETZKY, N. — "Saccocirrus papillocercus, uov. gen., n. sp.," 



'Mem. Soc. des Naturalistes de Kiew,' 1871. 



2. Fraipont, J. — " Le genre Polygordius," 'Fauna u. Flora des Golfes 



von Neapel,' vol. xiv, 1887. 



3. Fratpont, J. — "Lesystenie uerveux . . . des Archiaunelides," 'Arch. 



Biol./ vol. v, 1884. 



4. GiARD, A. — " Sur les affinites du genre Polygordius," ' Coniptes rendus,' 



vol. xci, Paris, 1880. 



' Giard seems to me to have been very near the truth when he wrote of 

 Polygordius, " C'est un type d'Aunelide archaique et aberrant" (4). 



