522 CUESSWPJLL SHEARER. 



only been observed reproducing (Zeppelin 27) by fission. 

 Possibly Ctenodrilus may be intermediate in position 

 between Polyg-ordius and Diuopliilus^ but the posses- 

 sion of distinct setfe sacs would seem to denote that it is a 

 degenerate Polychtet. Eisig (3) has also expressed the 

 opinion that Histriobdella is a very degenerate form and 

 not an Archiaunelid^ and it is possible that all the members 

 of this class are after all very degenerate forms, in which 

 their simple structure is by no means primitive. This would 

 seem to be borne out by a number of features in their deve- 

 lopment. In Dinophilus and Histriobdella, certainly 

 the most interesting forms of this group, the direct mode of 

 development affords unfortunately little evidence of their 

 affinity, and what can be obtained from this source seems to 

 point to their being degenerate forms, as Eisig holds to be 

 the case. 



I. GeNEEAL DESCRirXION OF THE NeI'HEIDIA. 



The nephridia of Dinophilus can be satisfactorily 

 examined by placing the living worm on a glass slide and 

 covering it with a cover-glass to hold it and prevent excessive 

 movement. The most convenient method of doing this is to 

 support the cover-glass by a little soft wax which prevents 

 the worms from being crushed too much, but at the same 

 time allowing of their being compressed as required. The 

 structure of the nephridia can then be readily investigated 

 under an oil-immersion lens. As the nephridia frequently 

 run through the testis, which forms the largest part of tlie 

 body tissue in the male (see fig. 14) it is sometimes necessary 

 to examine the preparation from both sides in order to follow 

 a particular nephridium throughout its entire course. For 

 this reason I soon discarded ordinary glass slides for making 

 my preparations, and adopted big cover-glasses such as those 

 used for making large embryological slides ; the thinness of 

 the glass allows of the preparation being focussed under high 

 power lenses from either side as required. 



