PHYLOGENETIC ARRANGEMENT 171 



the two groups mentioned agree with Aeolosoma in having no oviducts; in all three 

 groups the ova are evacuated by pores or by a pore; but in the Enchytraeidae 

 there seem to be traces of the former existence of a proper oviduct ; fringes of cells 

 along the coelomic apertures of the oviducal pores seem to indicate the former 

 existence of proper oviducts ; the resemblance, in fact, may be more apparent than 

 real; as to the Naidomorpha we have but little information as to the exact nature 

 of the oviducal pores. With the Enchytraeidae Aeolosoma agrees in the origin of the 

 dorsal blood-vessel from a periintestinal sinus, and also in the presence of a cardiac 

 body; traces of this seem to occur in Aeolosoma tenebrarum; the same structure is 

 found in Ctenodrilus. Compared with the differences, the resemblances thus indicated 

 are but slight ; there is really no group of Oligochaeta with which Aeolosoma has 

 well-marked affinities ; I do not, therefore, think it unreasonable to place Aeolosoma 

 far away from the other Oligochaeta, a derivative of the Annelid stock before it had 

 thoroughly differentiated into the two groups, Polychaeta and Oligochaeta. I should 

 leave it aside, in fact, in considering the origin of the remaining groups. 



As to these remaining groups, they are undoubtedly all nearly connected ; 

 divisible though they are into Mici-odrili and Megadrili, there are no fundamental 

 differences of structure. It is, in fact, perhaps a little doubtful into which division 

 Moniligaster should go. We may, therefore, fairly consider them together with 

 three possible conclusions in view: (i) that both Megadrili and Microdrili are 

 derivable from a common stock ; (2) that the Megadrili have been derived from 

 the Microdrili; and (3) that the reverse mode of development has occurred. 



First, as to structural characters which may fairly be regarded as indicating 

 a low position; it is necessary to carefully eliminate those characters which may be 

 due to degeneration; it would be absurd, for example, in my opinion, to consider 

 Perichaeta hilgendorfi a primitive Perichaeta on account of the fact that it has no 

 spermiducal gland, present in nearly all the other species of the family ; no doubt 

 the presence of this gland is a secondary character; but in the particular case 

 under consideration its absence must be secondary. One naturally turns to the 

 reproductive organs for a clue to the difficulties of phylogeny. Considering that the 

 reproductive ducts are developed from the nephridia of successive segments (in 

 Octochaetus at any rate), it might be fairly supposed that the closer the correspondence 

 between the ducts, the more primitive would be the characters of the worm ; the 

 differences between the male and female ducts must, one would think, be secondary. 

 Judged by this standard, Phreoryctes would have to be placed in the position of 

 the most archaic form of Oligochaeta ; it is particularly worthy of note, in connexion 

 with this matter, that the male-ducts of Phreoryctes, although longer than, and 



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