140 NOTES ON THE ANATOMY OF DINOPHILUS. 



pi. xxix, fig. 3) and obviously comparable with the vesiculee seminales 

 of Dinophilus. As in the latter animal, the vesicles open by ducts 

 into a median organ, supposed by Foettinger to be copulatory, and 

 o£ very complicated structure. No communication between the 

 vesicles and the body-cavity or testis is described. Anteriorly the 

 generative segment has a pair of lateral eversible penes. The exist- 

 ence of three separate copulatory organs in Histriodrilus recalls the 

 condition met with in some Polyclads [Anonymus, Thysanozoon) ,yv]ieYe 

 more than a single penis is found. 



The above facts, together with other well-known and striking 

 resemblances between Dinophilus on the one hand and Protodrilus, 

 Polygordiiis, or Histriodrilus on the other, make it in the highest 

 degree probable that Dinophilus is a true Archiannelid, as has been 

 insisted on by so many of the more recent writers on the subject. 

 In the number of segments, in the segmentation of the ventral 

 nervous system, and in the arrangement of the muscular system, of 

 the nephridia, and of the generative organs, Dinophilus more nearly 

 approaches Histriodrilus than any of the remaining Archiannelids. 

 On the other hand, in the chai-acter of the muscular appendage of 

 the oesophagus, in the wide separation of the ventral nerve-cords, 

 and in the method adopted by the female for laying its eggs, Dino- 

 philus most closely resembles Protodrilus. Although Dinophilus 

 seems so clearly an Archiannelid, it is nevertheless possible to hold 

 with Korschelt, Weldon, and others that it gives evidence of having 

 been derived from Platyhelminth-like ancestors. 



Weldon (13) has called special attention to the significance of the 

 muscular oesophageal appendage as a representative of the pharynx 

 of a Planarian. The median position of the generative pore, and 

 the method of fertilization adopted by the male Dinophilus tssniatus, 

 further support the view of the Platy helminth origin of the Archian- 

 nelids. The median penis of D. tseniatus and D. gyrociliatus is 

 strictly comparable with the same structure in a Planarian, although 

 it is probably a highly significant fact (if this is really the case) that 

 this organ has entered into relations with a pair of modified nephridia 

 which receive the spermatozoa from the testes. 



Korschelt (6) and others have drawn attention to the remarkable 

 fact that, whilst the female of one species of Dinophilus differs com- 

 paratively little from that of any other species, there are very great 

 differences between the males of the various species. In D. gyro- 

 ciliatus (including D. apatris) (and possibly in D. metameroides , in 

 which the male is not known), there is very striking sexual dimor- 

 phism, the female being many times larger than the male. In 

 D. vorticoides, D. gigas, and D. tseniatus, on the contrary, the males 

 do not differ appreciably in size from the females. Whilst in D. gigas 



