BY H. L. KESTEVEN. 685 



endo-niesoderm "anlage" is early recognisable, but only in the early 

 naupliiis-stage, does it become possible to separate endoderm and 

 mesoderm. 



It is worthy of note that histogenesis has not progressed so far 

 in Ubius at the nauplius stage as in Chondracanthus. This differ- 

 ence is most striking at the posterior end. In Ubius the ectoderm 

 is so extremely thin as to be actually doubtfully present at the 

 extreme posterior end, whilst the mesoderm-belt is composed of not 

 more than twenty-five large cells. In Chondracanthus, the ecto- 

 derm is so well developed that the rudiment of the ventral ganglion 

 (Bauchganglienanlage) may be identified. Mesoderm and endo- 

 derm, however, are not so far advanced in differentiation. 



Comparative. — A brief comparison with Ive balanoglossi Mayer, 

 has already been made in the generic description; in view of 

 their close relationship and similarity, it may be well to tabulate 

 the outstanding differences. 



Ive balanoglossi. Ubius hilli. 



Body presenting annular Body cylindrical, without 

 thickenings, suggesting segmen- trace of segmentation, 

 tation. 



Oesophagus chitin-lined. Oesophagus lined by colum- 



nar epithelium. 



Mid-gut strongly muscular. Mid-gut devoid of obvious 



muscles. 



End-gut lined by chitin. End-gut absent. 



Double ventral nerve-cord. No nerve-cord visible. 



Ovary single. Ovary paired. 



Testes large, reniform. Testes small, cylindrical. 



Systematic. — The systematic position of Ubius must remain more 

 or less in doubt, until the stages between the nauplius and the 

 adult are known; meanwhile, an attempt must be made to assign 

 it a position on the characters of the adult. Notwithstanding the 

 important differences between Ive and Ubius, it seems evident that 

 they both belong to the same family. I agree with Mayer that it is 

 not necessary to found a new family for the reception of Ive, but 

 unlike him, I am unable to see that its adult features point to a 

 relationship with Lerncea. 



