THE ANATOMY. NEPHRIDIA 



51 



The development of nephridia of the plectonephric type has been investigated 

 by myself in Odochaetus muUiporus. There is no doubt that the numerous nephridial 

 tufts of the mature worm with their numerous openings on to the exterior are 

 produced by the growth of a paired series of organs, which, as Vejdovsky thinks, 

 are probably the equivalents of the pronephridia of Luonbricus. These paired 

 nephridia, however, are provided with well-developed and ciliated nephrostoms ; 

 and in their course they are much coiled upon themselves before reaching the 

 external pore. The first pair are anomalous from the very earliest stage in which 

 I studied them. They occupy at least two segments as does the ' head- kidney' of 

 other species, and they open, not on to the lateral body surface but into the 

 commencement of the stomodaeum. A little later in the course of development 

 these first pair become fused with the second pair and the pore is more definitely 

 within the stomodaeal cavity, from which a tubular outgrowth appears to have 



Fig. 13- 



DEVELOPMENT OF NEPHRIDIAL TUFT OP MEGASCOLIDES. 



(After Vejdovsky.) 



J. Funnel. 2. Septum. 3. Nephridial tufts in various stages. 4. Connecting tubes finally 



(4 a) degenerating. 



arisen to meet the duct of the nephridium. Thus the ' mucous gland ' of the adult 

 worm is a compound structure representing, two nephridia of successive segments. 

 The funnels of all the pairs of pronephridia, at first functional, degenerate later ; 

 the cilia disappear and the row of cells which forms the funnel becomes more than 

 a single cell thick. The lumen of that part of the nephridium also which immediately 

 follows the funnel vanishes and a solid string of cells is left. 



The development of such nephridia has also been studied by Vejdovsky (4) in the 

 Australian earthworm Megascolides australis. There appears to be no doubt that in this 

 species there is (see accompanying woodcut) to begin with a pair of nephridia to each 

 segment ; these have a funnel and from the funnel leads a straight duct not perforate ; 

 here and there the cells become larger and finally form loops ; these loops ultimately 

 increase in size and become complicated coils, the connecting part of the original tube 



H 2 



