1907.] NATURAL SCIENXES OF PHILADELPHIA. 133 



although it seems pr(jl)al)le that it is one of those in the posterior part 

 of the body. From the evidence at hand it is seen that four of the 

 nine species of Dinophilus are composed of six segments (metameres), 

 counting the head, and this raises the question as to whether this 

 mmiber is characteristic of the group; the answer to wlucli must neces- 

 sarily be found in further research. 



Cepholization. — Among the evidences of specialization exhibited 

 by Dinophilus conklini is a well-defined tendency to cejihalization on 

 the part of the nervous system and the nephridia. A glance at fig. 1 

 will serve to show that this is true of the nervous system, especially 

 as regards the number of nerve cells. That a like tendency is exhibited 

 by the nephridia also will be plain on considering the great size and 

 complexity of the first pair of nephridia as compared with the succeed- 

 ing four. 



Relationships. — The systematic position and affinities of Dinophilus 

 have been long debated, and is a cjuestion concerning which every one 

 who has investigated this form has expressed an opinion. In a pre- 

 vious paper on the embryology of Dinophilus (1904a), I have given a 

 brief historical sketch of the various views expressed by different 

 authors on this subject, so it need only to be referred to here. Broadly 

 speaking, these views may be divided into three classes, according as 

 they regard Dinophilus as most nearly related to the Turbellaria, to 

 the Rotatoria, or to the Annelida. 



In respect to the morphological evidence on which the first of the'^e 

 views is based, Lang (1884) has summed this up so concisely and com- 

 pletely that I cannot do better than to quote his words in full: 



"I believe that Korschelt^ is on the wrong track; there are no Tur- 

 bellaria with an anus, none with ciliated rings. The pharanx of Di- 

 nophilus has nothing in common with the pharanx of the Turbellaria. 

 None of the Turbellaria have a straight alimentary canal so much 

 differentiated. The sex organs are constructed differently in the two 

 groups; in the Turbellaria complicated ducts are always present. 

 The sexual dimorphism removes Dinophilus from the 'Turbellaria, as 

 well as the well-developed body cavity. I do not believe that, as 

 Korschelt supposes, the ova arise from the epithelium of the alimentary 

 canal. They indeed lie in the body cavity close to the alimentary 

 canal, but I am strongly of the opinion that a fine endothelium is here 

 present, from which they develoj). Ever^'oue knows how difficult 



* Lang here refers to Korschelt's earlier view (1SS2). Korschelt has since 

 expressed the opinion that Dhiophilus is closely allied to the annelids 



