BY E. J. CxODDARD. 481 



In this connection it is noticeable that aiinuli 5 and 6 show 

 signs of fusion (complete on the ventral aspect), and that these 

 are determined as belonging to and really constituting somite iv. 

 Again, we find annuli 7 and 8, which represent the first two 

 annuli of somite v.(triannulate), are fused on the ventral aspect. 

 In the case of somite iv., the first annnlus has evidently dis- 

 appeared by fusion with annulus 5, which represents the middle 

 annulus of the originally pentannulate, and later triannulate 

 somite; and is oculiferous. In the case of somite v., we find 

 that abbreviation has not taken place to such an extent as in iv., 

 but still it is the first annulus, namely 7, which is showing signs 

 of fusion with the middle constituent of this somewhat abbreviated 

 (triannulate) somite. 



This is admirably in keeping with the generalisations made by 

 Castle for the Hirudinea in the matter of somite-extension or 

 abbreviation. 



Benham mentions, in his account of Hirudo maidana, that 

 annuli 5 and 6 are fused. 



Somite vii. is tetrannulate, the first annulus of the originally 

 pentannulate somite having disappeared, and the somite approach- 

 ing the condition of somites v. and vi., or that the perhaps more 

 primitive triannulate somite has added an annulus in its posterior 

 region and not in its anterior region. 



The order of abbreviation would then appear to be as follows : 

 Annulus. Ann. Ann. Ann. Ann. 



12 3 4 5 



(a) (c) ^ ^ {d) (b) 



Nephridiopores. — Nephridia do not occur in other than 

 tetrannulate or pentannulate somites. The first pair of nephri- 

 diopores lie on the first annulus (near its posterior margin) of 

 somite vii., that is, annulus 13. In contracted specimens the 

 nephridiopores would appear to open between two annuli — the 

 annulus bearing it and the succeeding one. The remaining 

 sixteen pairs of nephridiopores lie on the posterior margins of the 

 second annuli of the pentannulate somites viii.-xxiii: that is, they 

 lie on annuli 18,23,28,33,38,43,48,53,58,63,68,73,78,83,88,93. 

 49 



