772 PEOFESSOR J. STEPHENSON ON 



(1) Anatomical evidence in support of this position is not wanting in the case of 

 yEolosoma ; the cerebral ganglion remains attached to the superficial epithelium 

 throughout life, and the ventral nerve cord is absent, or, at any rate, only demonstrable 

 with difficulty as a rudiment. Again Vejdovsky (54) found in occasional specimens 

 of A. ehrenhergii { ^ heni'prichi) two fine lateral commissures given off from the 

 pharyngeal vascular ring, which he thought joined the dorsal vessel ; these might be 

 looked on as vestiges of lateral loops which in most individuals have entirely disap- 

 peared. As regards the Naididse, however, apart from certain peculiarities in the genus 

 CJisetogaster, which I have previously argued is descended from parasitic ancestors, I 

 cannot recall any features in the adult anatomy which point clearly to degeneration. 

 The same may be said of the Enchytrseidse, which, like the Naididse, have only a small 

 number of lateral commissures. 



The answer to the argument for the degeneracy of the lower families of the Oligo- 

 chseta would be that admitting it as probable for JEolosoma, at least as regards certain 

 features, still degeneration in respect of certain structures does not mean degeneration 

 in respect of all ; that Beddard himself (3) derives ^olosoma from the base of the 

 Oligochsete stock ; and that in any case degeneration has not been made out for the 

 Naididse and Enchytrseidse. At the same time Vejdovsky's observations quoted above 

 carry weight as regards the decision of the question in jEolosoma. 



(2) The prevalence of asexual reproduction in JEolosoma and the Naididse may 

 be used as an argument for their degeneracy. Thus Beddard (3, p. 170), for ^Eolosoma, 

 adduces the statement of Meyer, that asexual reproduction only occurs in undoubtedly 

 degenerate forms, or in those forms where sexual products abound in the posterior as 

 well as the anterior part of the body. But Meyer's position is, I think, difficult to 

 substantiate, and the statement is probably too sweeping ; and to use it in support 

 of the present contention is to take for granted the precise point at issue. Moreover, 

 the argument does not touch the Enchytrseidse. 



(3) Beddard (3) quotes Bourne's observations (8) on Uncinais littoralis, in 

 which species a regular series of loops was found to be present in the budding zone of 

 those individuals which were reproducing by fission. Beddard, using the word "bud " 

 apparently in the sense of a young individual, states (from Bourne) that "in the 

 young buds commissural vessels occur in all the segments " [loc. cit., p. 295 ; cf. also pp. 

 72, 277, in the same sense), most of which vessels afterwards disappear. It is inferred 

 that phylogenetically, also, the Naididse as a family primitively possessed an extensive 

 series of loops reaching to the posterior end of the body, and that these have secondarily 

 become reduced in number. 



It is necessary, in order exactly to understand the position, to refer to Bourne's 

 original description, and especially to his figures. We have not a complete account 

 of the history of these loops ; but what Bourne states, and what his figure shows, is 

 that the loops are present in the actively growing regions of the worm, i.e. the zone 

 of budding and the posterior end of the animal. It is, however, clear that no individual 



