638 MR FRANK E. BEDDARD ON THE 



Vejdovsky [A 11, p. 1G3] considers that it is most nearly related to the Tubificidge 

 (Limnodrilus). This conclusion was arrived at without any knowledge of the reproductive 

 ducts which were at that time unknown ; their discovery renders that particular view of 

 the affinities of Phreoryctes less satisfactory than it would otherwise be. 



It is also important to notice that in some respects the reproductive ducts of the 

 adult Phreoryctes recall those of immature forms of other Oligochseta. For example, in 

 Tubifex, the development of whose reproductive organs has been carefully worked out by 

 Vejdovsky [A 11], the atrium, which forms so important a part of the adult efferent 

 system, is very inconspicuous to begin with. In the young Tubifex [A 11, pi. ix. fig. 

 18] it is represented by a very small dilatation, and the vas deferens itself is a short 

 straight tube without any trace of the complicated windings which characterise the vas 

 deferens of the sexually mature Tubifex. I have, myself, pointed out that in Clitellio 

 arenarius [B 1] the vas deferens is at first short and straight, and afterwards becomes 

 much longer and coiled several times, though its windings are never so complex as those 

 of Tubifex. Psammoryctes [Vejdovsky, A 11, pi. x. fig. 17] is another instance to the 

 point. 



A comparison between the vasa deferentia of the adult Phreoryctes and those of the 

 young Tubifex, Clitellio, &c, is not vitiated by the suggestion that the resemblance is a 

 purely superficial one, brought about by the fact that the more complicated vasa deferentia 

 of Tubifex and Clitellio must necessarily pass through a stage such as that described ; 

 that it is merely "the way they develop," and is void of any significance, just as some 

 naturalists have attempted to show that the Nauplius is of no phylogenetic significance, 

 inasmuch as a Crustacean with nineteen pairs of appendages developing progressively 

 must pass through a stage in which there are only three pairs. 



In the case of the vasa deferentia there does not appear to be any a priori reason 

 why the course of development should be as described, unless it has a phylogenetic 

 significance. The nephridia of Tubifex, whose development Vejdovsky has also worked 

 out, form a series of loops nearly as complicated as those of the adult before the con- 

 nection with the distal vesicle is established [cf A 11, pi. ix. figs. 1, 2], 



Bergh's [B 2] observations upon the developing nephridia of Criodrilus are, as regards 

 this point, confirmatory of the statements of Vejdovsky ; the nephridia arrive at some 

 degree of complication before the external orifice is formed. Arguments of this kind, 

 however, will not, in my opinion, apply to the atrium ; the appearance of this organ in 

 many Oligochseta before the development of the vasa deferentia, and its almost universal 

 presence and large size, indicate that it is a very characteristic organ in this group. Its 

 full development, therefore, in Phreoryctes is not to be compared with the full develop- 

 ment of the atrium in the immature Tubifex, but is due to degeneration. 



The reproductive organs of Phreoryctes are, therefore, to be regarded as being on the 

 whole archaic in characters, but to have undergone some modification in the nearly 

 complete disappearance of the atria. 



It follows, from what has been said in the foregoing pages about the reproductive 



