180 



Tratisdctions. 



le- 



(25) 

 tei-- 



woniis of vaiiouti families, is indicated by its large nucleus, sunouuded by 

 granular pi'otoplasiu. But what makes this funnel of Muoridrilus rosae 

 remarkable is the gi'eat tuft of cilia l)f)rne l\v this central cell, and directe 1 

 down the nephrostomial canal : for in other earthworms this central canal 

 is not ciliated.* 



These cilia represent probably the original cilia of the flame-cell which 

 terminated the pml)ryonic nephridium : they have become somewhat 

 reduced in size, and increased in number with the co^ 



inci^easing size of the cell, but have still retained 

 theii' original direction down the funnel. If this be 

 so, the cilia I'epi'esent an interesting case of the sui'- 

 vival of an old structure in the specialized organ 

 which has been developed from the older and simpler 

 form. The presence of these cilia on the central cell 

 is most unusual. 



On reference to Vejdovskys figures of the 

 velopment of the nephridia of Rhynchelmis 

 we find that the embryonic pronephridium 

 minates in a large cell containing a vacuole, 

 in which the flagellum forming the '' flame " 

 projects downwards towards the nephridial lobe, 

 composed of a string of cells without lumen. As 

 the embryo grows into the adult worm the vacuole 

 acquires an opening to the coelom and becomes 

 the cavity of the funnel, while the terminal cell 

 forms the central cell of the funnel of the adult. 

 In the case of Maoridrilus the development is 

 probably similar, and the cilia have persisted on 

 the central cell, which forms the chief poi'tion of the 

 upper lip, as does the terminal cell in Blufuchelmis. 



Ltimhriciis, on the other hand, has a terminal cell 

 in its embryonic pronephridium devoid of vacuole 

 or flame ; here, then, is perhaps the reason for the 

 absence of cilia on its central cell. 



The post-septal portion of the nephridiun (tigs. 6 

 and 8) consists of two folds, anterior (a.f) and pos- 

 terior (p.f) respectively, a large terminal liladder (hi). 

 and a smaller fold, or " spur " {sp), which comes off 

 from the ventral end of the posterior fold. 



The anterior and posterior folds are connected by 

 a single tubule, the " bridge "" (h), which is ciliated 

 throughout its length (tig. 8) ; and the anterior fold 

 is connected with the bladder by a single Avide duct, 

 the " outlet-duct "' {o.d). 



The anterior and posterior folds consist of tubules 

 embedded in connective tissue ; they lie parallel to 

 each other, and transversely across the body. I 

 have used the nomenclature given by Eisen (17), 

 but these two folds together correspond to the 

 second or middle loop of Lumbricus (10). The single 



* The general shape of the funnel recalls that of many 

 of the Enchytraeidae, but in them the long cilia (? borne By 

 the central cell) project freely through the opening. (Vida 

 VejdovHkv, Eisen.) 



Fig. (). 

 Outline; of dorsal nephridium 

 mounted in glycerine. The 

 covering of coelomic e})ithe- 

 lium (c.ep) is shown in part ; 

 the bladder is turned over, 

 so that the pore appears to 

 be facing the posterior m- 

 stead of the anterior end of 

 the segment. 



