1'ROF. W. A. HASWELL : THE EXOGONECE. 217 



The Exogonece. By W. A. Haswell, M.A.. D.Sc, F.R.S., F.L.S., 

 Emeritus Professor of Biology, University of Sydney. 



(Plates 17 & 18, and 2 Text-figures.) 



[Read 5th December, 1919.] 



Introduction. 



In the introductory part of his ' Recherches sur les Syllidiens' (1913), 

 Malaquin has embodied a very complete history of the development of our 

 knowledge of the family. Malaquin's own work is certainly of the first im- 

 portance in connexion with this development, on account both of the original 

 observations recorded therein and of the systematising of work previously 

 published. But. Malaquin concerns himself almost exclusively with the 

 Eusyllidea, the Syllidea. and the Autolytea, having few actual observations 

 on the Exogonece to record : and out of three hundred and fifty or more 

 figures with which the work is illustrated only three refer to the Exogonece. 

 Thus in his account of the alimentary canal, the nephridia and gonads, and 

 the development, it is almost assumed that the Exogonece resemble the larger 

 forms but for the difference in size. And this is quite true np to a certain 

 point. But beyond that, in a number of important details the Exogonece, or 

 certain of them, present very special features. 



The material on which the following observations were based was collected 

 almost exclusively in Port Jackson, either between the tidal limits or a little 

 below low-water mark. 



In the structural part I have not given any general account of the mor- 

 phology ; but have confined myself to certain sets of organs with regard to 

 which the Exogonece exhibit peculiarities of a strongly-marked character — the 

 integumentary and related glands, the alimentary canal, and the nephridial 

 and reproductive organs. 



In the account of the embryology which follows there are various obvious 

 gaps. I hope to fill some of these later by the adoption of certain methods 

 which I have not hitherto utilized ; the detailed history of the cell-lineage, 

 for example, can only be followed out by keeping large numbers of living 

 specimens under observation. As it is, however, the study of my extensive 

 collection of fixed material has resulted in the observation of a number of 

 facts which have hitherto, so far as I have been able to ascertain, been 

 unrecorded. 



I have pleasure in acknowledging my great indebtedness to Professor 

 Mcintosh for literature, specimens, and information furnished ; to Professor 

 Benham for the loan of his copy of Malaquin's work ; and to Dr. Pierantoni 



