ON PHYMOSOMA VARIANS. 95 



(12) The animals are dicecious. The generative organs 

 are in the form of ridges at the base of the ventral retractors. 

 The flat ccelomic epithelium is here modified to give rise to 

 ova in the females and the sperm morulas in the males. 



Conclusions. 



I do not propose to consider at any length the theoretical 

 conclusions which might be drawn from the facts above indi- 

 cated until I have worked out in detail other forms of the 

 Gephyrea, which I hope to do in the immediate future. I 

 should, however, like to say something in favour of maintain- 

 ing the genus Phoronis in its old position — that is, as a form 

 closely allied to the more normal Gephyrea inermia. 



This relationship is most easily seen by comparing a view of 

 the head of Phymosoma as seen from above with a view of 

 Phoronis (figs. 31 and 32). In both genera the mouth is sur- 

 rounded by a pair of vascular horseshoe-shaped ridges, one of 

 which is dorsal and the other ventral : the sole point of difference 

 lies in the fact that while in the one case the tentacles of the 

 lophophor extend along both the ventral and the dorsal horse- 

 shoe, they are in the other case confined to the dorsal limb. 



Again, the prseoral lobe of Phoronis bears two large 

 sensory pits, one on each side of the middle line ; these are 

 obviously comparable to the similar pits which open into the 

 area in the concavity of the Gephyrean lophophor which I 

 have spoken of as the prseoral lobe. Further, the nervous 

 system of Phymosoma, like that of Phoronis, is permanently 

 connected with the epidermis. 



I do not enlarge upon the resemblances in the position of 

 the anus, and the lengthening of the ventral surface at the 

 expense of the dorsal, or on the presence of two nephridia, as 

 these points have been already emphasized by Lankester. 

 But I would direct attention to two structures hitherto, I 

 believe, undescribed in the Gephyrea, which in my opinion 

 have homologues in Phoronis. 



The first of these is the skeletal tissue ; this, as the descrip- 



