r.H)7.] NATURAL SCIENCES OF PHILADELPHIA. 135 



(lass ini Uauc dos Xorvcnsystems uiul der Hauptmusculatur der Rota- 

 torieii die Tendenz zur Er\verl)un<i- der Metamerie l)enierkt warden 

 kann: bei Dinophilus abcr erstreckt sich diese Tendenz aucli auf das 

 Mesoderm und die Excretionsorgane. Aueh hci den Rotatorien 

 erscheinen, wic hei DinnpJiilus die Genitallu'ihlen als einzige Homologa 

 des Coelonis." 



According to this view the metamerism, as well as many other 

 annelidan features, would have to be regarded as having arisen inde- 

 pendently. From this standpoint Dinophilus would, so far as its 

 resemblance to annelids is concerned, be a good example of convergence. 

 In regard to the points of reseml)lance which Schimkewitsch has pointed 

 out : the segmentation of the egg has been shown to be strictly annelidan 

 in its type. The caudal appendage of Dinophilus much more closely 

 resembles that of some polytrochal annelid larvfp than the foot of the 

 Rotatoria. The sexual dimorj^hism quite clearl}' arose within the 

 group, and is one which is found in other groups than the rotifers. The 

 condition of the sex organs in the less specialized members of the 

 Dinophilicke (e.g., D. vorticoides) Meyer (1901) regards as representative 

 of the primitive condition of the ccelomesoblast in the annelids, and 

 one which is ciuite different from that found in rotifers, since the 

 unpaired condition found in D. conklini is evidently a derived one. 

 Moreover, the opinion is widely held that the Rotatoria constitute a 

 highly specialized group of somewhat uncertain affinities, since much 

 doubt has been thrown on its formerl}'- assumed close relation to the 

 trochophore. In short, when the various morphological characters 

 can be duplicated within the annelids, or accounted for by derivation 

 from that ancient and primitive group, it seems superfluous to suppose 

 that they have arisen independently, and to derive Dinophilus from 

 such a comparatively specialized group as the Rotatoria. 



Dinophilus has also been often compared to the trochophore larva of 

 annelids, but this comparison is somewhat inexact, if the term trocho- 

 phore is employed in the strictest sense. The resemblance is rather 

 to that intermediate stage in the metamorphosis represented by some 

 larvae of the potytrochal type. The head of Dinophilus is, for example, 

 in no way comparable to the inflated cephalic vesicle of the typical 

 trochophore; the trunk with its various organs is distinctly metameric, 

 and therefore to be compared with the trunk of the worm. On the 

 other hand, such features as the ciliated bands, particularly those pre- 

 oral in position, the ventral ciliated tract, and the preoral commissure, 

 have obviously been derived from the trochophore stage. On the 

 \Ahole, Dinophilus can l)est be considered as a veiy young polychsete 



