ON A NEW ORGAN IN THE LYCOEIDEA. 399 



this, then we must be prepared to explain what has become of 

 the genital ducts with which the ancestors of these Chaetopods 

 were provided before their nephridia opened inwards, and why 

 these ducts have disappeared leaving no trace behind them. 

 On the other hand, I think that this difficulty may be avoided 

 if we consider the original genital duct to have been a simple 

 outpushing of the coelomic epithelium which opened to the 

 exterior, and afterwards became more or less grafted on to the 

 nephridium.i Whether the coelom in the Cheetopods was primi- 

 tively ciliated all over — as, for instance, in Rhynchobolus — is a 

 very interesting question suggested to me by Professor Lan- 

 kester. If this was the case the ciliated organs might have 

 been formed by the restriction of the cilia to a definite area, 

 bringing with it the specialisation of the epithelium and the 

 development of a definite organ for a particular function. 



In conclusion, I wish to express my thanks to Professor 

 Lankester and Dr. Benham for their constant help and advice 

 throughout my investigations. 



List of Works referred to. 



1. Benham. — " The Nephridiuni of Lumbricus," ' Quart. Journ. Micr. 



Sci.,' xxxii, 1891. 



2. Claparede. — 'Les Annelides Chetopodes du Golfe de Naples,' Suppl., 



1870. 



3. CosMOVici. — '• Glandes geuitales et organes segmentaires des Annelides 



Polych^tes," 'Arch, de Zool. exp. et gen./ viii, 1879-80. 



4. Cunningham. — " Some Points in the Anatomy of Polycheeta," ' Quart. 



Journ. Micr. Sci.,' xxviii, 1887. 



5. Ehlers. — "Die Borstenwiirmer," Leipzig, 1864-8. 



6. EisiG. — ' Die Capitelliden des Golfes von Neapel,' Berlin, 1887. 



7. Kowalevsky. — "Ein Beitrag zur Kenntniss der Exkretionsorgane," 



'Biol. Centralblatt,' ix, 1889. 



8. Meyer. — "Studien iiber den Korperbau der Anneliden," 'Mittheil. 



Zool. Station Neapel," vii and viii, 1887-9. 



> Since this was printed I have found that E. Meyer put forth very 

 much the same theory in 1890 ("Die Abstammung der Anneliden," 'Biol. 

 Central.,' x). 



