490 EDWIN S. C400DR1CH. 



The posterior canal grows to the surface, where it opens through 

 the epidermis ; in some cases there is here an invagination of 

 the epidermis to form the end-vesicle (Yejdovsky). 



As to the origin of the funnel-cell — the forecast of the whole 

 true nephridium : it arises from the primitive cell row, or 

 nephric cord, formed by the repeated division of one of the 

 teloblasts on either side. In the earlier stages this teloblast 

 and the nephric cord to which it gives rise lie on the surface of 

 the embryo; thus the funnel-cells are epiblastic in origin. 

 From the nephric row one cell enlarges and enters into con- 

 nection with each successive segment, as described above (fig. 5). 

 To judge from the figures of Bergh, Wilson (108 and 109), and 

 Vejdovsky, in some forms, such as Dendrobsena and Lumbricus, 

 the funnel-cells give off the chain of posterior cells, whilst 

 separating from the nephric row, thus remaining for some time 

 in connection with it. In other cases, such as Criodrilus, the 

 funnel-cells appear to separate first.^ 



In the embryo of most Oligochsetes the nephridia of the 

 first segment are developed precociously to perform the 

 excretory functions at an early stage (fig. 25). Vejdovsky 

 (100 and 101) has described these organs in Rhynchelmis, 

 Chaetogaster, ^olosoma, Nais, Allolobophora, Lumbricus, 

 Dendrobsena, &c.j and Bergh described those of Criodrilus (9). 

 They consist of fine canals with an intracellular lumen, or some- 

 times of wider tubes; they'are often ciliated, and occasionally end 

 internally in a flame-cell ; they appear to be always blind 

 within. Externally they open either by a median dorsal pore 

 or by two lateral pores on the first segment. In fact they 

 closely resemble the closed pronephridia of the Flatyhelmiuths, 

 Entoprocta, and other groups we have already examined, or tlie 

 pronephridial stage of the trunk nephridia. 



The origin of the cells which form the (larval) nephridia of 

 the first segment has not been traced; but since they arise (in 

 some cases at least) before the division of the promesoblast cell, 



' Bergh denies the derivation of tlie funnel-cell from the nephric row. 

 Wilson rightly traced the development of the main body or canal of the nephri- 

 dium from the nephric row, but failed to discover the origin of the funncl- 

 oell itself. 



