SOME POINTS IN THE ANATOMY Ob' FULKUHAiTA. 239 



On Some Points in the Anatomy of Polychaeta. 



By 



J. T. Cunningham, B.A., F.R.S.E., 



Fellow of University College, Oxford. 



With Plates XVII, XVIII and XIX. 



1. Nephridia and Gonads. 



Before the year 1880 it had been conclusively shown by the 

 results of various researches that a " segmental organ " was a 

 glandular tube, either simple or convoluted, ciliated through 

 the greater part of its length, having internally a ciliated 

 funnel-shaped opening by which it communicated with the 

 body cavity, externally an opening to the exterior. The func- 

 tion of the segmental organ had been shown to be excretory, 

 depurative, but it had also been proved that in some cases at 

 least the organ served as efferent duct for the reproductive 

 elements. The segmental organs in their typical form had 

 been found principally in the Chaetopoda, but it had been 

 shown that the tubular glands known as the " Organs of 

 Bojanus *' in Mollusca conformed in all essential features to 

 the plan of a segmental organ, though they did not as a rule 

 act as genital ducts. 1 Notwithstanding that these facts had 



1 The generalisation that excretory tubes similar to " segmental organs," 

 were homologous structures in whatever division of the animal kingdom they 

 occurred, was formulated by Lankester in 1877, in his " Notes on Embryo- 

 logy and Classification," published in this Journal. To the morphological 

 element so defined he gave the name Nephridium, as applicable in every case. 

 This view of the original morphological identity of excretory organs was con- 

 firmed by the discovery of typical nephridia in Peripatus, which was made by 



