494 EDWIN S. GOODRICH. 



ARCHIANNELIDA and PoLYCHjETA. 



The first origin of the iiephridia in these worms is not so 

 well known as in the case of the Oligochseta. It is, however, 

 to be remarked that in the only case where the forecast of the 

 nephridium appears to have been traced from the beginning, 

 it has been found to arise from the epiblast (the head-kidney 

 in Nereis; Wilson, 110).^ This would agree with what we 

 have seen occurs in most, if not all, of the groups we have 

 already examined. 



E. Meyer (80) has given us a most excellent description of 

 the development of the nephridia in Polymnia and Psygmo- 

 branchus. They arise on either side from large cells, situated 

 close to the epiblast between each pair of mesoblastic somites, 

 with which they have no connection at this early stage. These 

 large cells, which seem to me obviously homologous with the 

 " funnel-cells " of the Oligochfeta and Hirudinea, divide, form- 

 ing a short chain of cells within which an intracellular lumen 

 becomes hollowed out (figs. 10, 11, and 26). The mesoblastic 

 somites become hollowed out to form the genital or ccBlomic 

 follicles, from the posterior wall of which the coelomic epithe- 

 lium becomes pushed out, forming a typical ciliated peritoneal 

 funnel, which fuses with the internal blind end of the nephri- 

 dium (figs. 11 and 26). This specialised portion of the coelomic 

 epithelium forms the wide-mouthed funnel of the adult nephri- 

 dium (fig. 12). The lumen of the nephridial duct becomes 

 intercellular by the multiplication of the cells which constitute 

 its wall, and breaks through at its point of junction with the 

 funnel on the one hand (opens, in fact, here into the coelom), 

 and establishes a communication with the exterior through the 

 epidermis on the other. Such is the history of the wide- 

 mouthed segmental organs of compound origin of the trunk. 

 The nephridia of the first segment (or sometimes of several 



' Hatschek (48, 51, 54), Salensky (91), and von Drasclie (27) all consider 

 the cells from which the nephridia are developed to be of mesoblastic origin, 

 but the evidence on this point is not convincing. Possibly, however, as sug- 

 gested for the MoUusca, they have secondarily come to be derived from the 

 mesoblast. 



