MR PRANK E. BEDDARD ON THE ANATOMY OF OCNERODRILUS. 581 



As regards the facts of structure enumerated in the above Table, it appears that 

 Ocnerodrilus shows no affinity to any one of the three genera in particular ; it cannot be 

 said to come nearest to Pontodrilus, or to Microscolex, or Photodrilus. 



It differs from all of them in the following characters : — 



( 1 ) Greater extent of the clitellum. 



(2) Setse strictly paired. 



(3) Gizzard totally absent (?as to Photodrilus). 



(4) Spermathecse without diverticulum. 



(5) Atrium lined by a single layer of cells. 



(6) Absence of a vascular network upon the nephridia. 



The last four characters, which are evidently the most important, show a further 

 simplification in the structure of Ocnerodrilus as compared with its nearest allies among 

 the Cryptodrilidse. This simplification of internal structure is in the direction of 

 many families belonging to the aquatic Oligochseta, to none of which, however, is there 

 more than a general resemblance, brought about merely by this simplification. 



Our present knowledge, however, of the aquatic Oligochseta is much less than of the 

 terrestrial forms ; nothing can be said as to the position which Ocnerodrilus occupies 

 with regard to the aquatic families until some link -turns up which may give a clue. In 

 the meantime it is evidently some way removed from even the simplest forms of one 

 group of Earthworms to a distance which appears to me to be sufficient to need the 

 formation of a special family for its reception. The family may be thus defined : — 



Family Ocnerodrilidce, Eisen. 



Small Oligochseta, with paired setse of Lumbricid pattern. Testes, two pairs in X and 

 XL Vasa deferentia open on to segment XVII, in company with an atrium lined by a 

 single layer of cells only, and divided into a glandular and non-glandular portion. 

 Ovaries paired in segment XIII ; oviducts opening on to segment XIV. Ova moderately 

 large ; septal glands present, but no gizzard. A single pair of glandular diverticula of 

 oesophagus in IXth segment. Nephridia abortive in some of the genital segments ; in 

 the posterior region of the body, imbedded in a mass of large vesicular peritoneal cells. 



Genus Ocnerodrilus, Eisen. 



Ocnerodrilus, Eisen, Nov. Act. R. Soc. Upsal., 1878. 



Clitellum extensive, inclosing the reproductive pores. 



One or more pairs of spennathecse in anterior segments, without diverticula. No 

 penial setse. Vascular system consisting of a dorsal and ventral trunk, and two lateral 

 vessels given off from dorsal vessel in the Vllth and VHIth segment. Two large hearts 

 in segments X, XL 



