ANATOMY, HISTOLOGY AND AFFINITIES OF PHREORYCTES. 639 



organs of the Oligochseta, that Phreoryctes stands midway between earthworms and the 

 majority of those forms which were formerly grouped together as Limicolse. It has 

 retained the paired testes and vasa deferentia of the former, while the vasa deferentia 

 are shortened ; the paired ovaries and oviducts of Phreoryctes are represented in a few 

 earthworms, but not in the lower aquatic Oligochseta. 



The clitellum again is more extensive than is the case with the lower forms, though 

 as in them it consists of but a single layer of cells. 



The paired setse with simple hooked (not bifid) extremities are characteristic of the 

 higher Oligochseta and of Phreoryctes. 



The structure of the body-wall in Phreoryctes, as regards the longitudinal muscular 

 layer, is more like that of earthworms. 



On the other hand, the sperm-sacs and ovisacs as well as the large size of the ova, 

 recall the Tubificidse and other families of aquatic or limicolous Oligochseta. 



Phreoryctes must therefore be regarded as occupying a position at about the middle 

 of the series ; it has retained some of the characteristics of earthworms, but has in other 

 respects acquired the simpler structure of the aquatic Oligochceta. 



It is, in fact, one of those forms which render a division of the Oligochseta into two 

 groups, " Limicolce " and " Terricolcs," impossible ; it could not be definitely referred to 

 either. 



LIST OF MEMOIRS REFERRED TO. 

 A UPON PHREORYCTES. 



1. Beddard, F. E. On the Reproductive Organs of Phreoryctes, Annals and Magazine of Natural 



History, June 1888. 



2. Claparede, Ed. Recherches sur lAnatomie des Oligochetes, M&moires de la Soci4U de Physique 



et d'Histoire Naturelle de Geneve, t. xvi. (1862). 



3. Giard, A. Fragments Biologiques X. Sur une nouvelle station de Phreoryctes Mcnkeanus, 



Hoffmeister (Eaux de Source de Douai), Bulletin Scientifique de la France et de la Belgiquc, 

 iii e ser., i re Annee (1888), p. 298, and idem, 2 e Ann^e (1889), p. 171. 



4. Hoffmeister, W. Beitrage zur Kenntniss deutschen Landanneliden, Archiv fur Natur- 



geschichte, Bd. i. (1843). 



5. Hoffmeister, W. Die bis jetzt bekannten Arten aus der Familie der Regenwurmer, 4to, 



Braunschweig, 1845. 



6. Leuckart, R. Berichte liber die Leistungen in der Naturgeschichte der niederen Thiere 



wahrend des Jahres 1859, Archiv fur Naturgeschichte, Bd. 26, 1860, p. 117. 



7. Leydig, F. Uber Phreoryctes Menkeanus nebst Bemerkungen, &c, Archiv fur miJcroscopische 



Anatomic, Bd. i. (1865), p. 249. 



8. Noll, F. C. Uber einen neuen Ringelwurm des Rheins, Archiv fur Naturgeschichte, Bd. xl. 



(1874), p. 260. 



