No. I.] GERM-LAYERS IN CLEPSINE. 165 



from, or in connection with, the nephric cell-cords, the general 

 uniformity in their position, their non-metameric character, 

 their atrophy and replacement by the permanent, metameric 

 nephridia, appear to indicate that they all belong to one and 

 the same system of organs. So far I am in accord with Bergh 

 (No. 9, pp. 269-272, and No. 30, p. 1 16) ; but I am not of his 

 opinion that this conclusion makes it impossible to homologize 

 the larval with the permanent organs. 



2. Significa7ice of Nephric Cell-Cords. 



The important bearing of the discovery of nephric cell-cords 

 on the question of the derivation of the vertebrate nephric 

 system has been ably presented by Wilson. Without entering 

 into the discussion of this side of the question, I may say that 

 I fully concur in his general views on this subject. There is 

 one point only to which I will briefly call attention. If both 

 the provisional and the permanent nephridia arise from the 

 same cell-cords, how are we to know, from the occurrence of 

 such cords, which system, if either, has been retained in tne 

 vertebrates? We may, as it seems to me, be quite certain about 

 the homology of the nephric cell-cords, and yet be quite unable 

 to decide whether one, both, or neither of the two nephridial 

 systems seen in the annelids is represented in the vertebrates. 

 We are not even certain that the larval nephridia represent the 

 same system throughout the annelids. The mode of origin of 

 the larval organs in leeches, as lateral-buds, reminds one of the 

 formation of the pronephros in Petromyzon ; but the outgrowths ^ 

 from the " segmental duct " have a metameric arrangement. 

 In the formation of the permanent nephridia of leeches we 

 have the metameric arrangement without the lateral outgrowths, 

 the entire cell-cords being cut up into consecutive cell-plates. 

 The fundamental importance of homologous nephric cell-cords 

 is not, however, lessened by any such difficulties in identification 

 as are here presented. 



* Scott (Morph. Jahrb. VII.) states that the pronephric funnels arise as outgrowths 

 from the segmental duct, while Shipley (Quart. Jour. Mic. Sc. XXVII., Jan., 1887, 

 p. 344) represents them as arising from a groove in the parietal peritoneum. As this 

 groove (which is continuous with the lumen of the segmental duct) closes up, it leaves 

 four or five openings which persist as the openings of the ciliated funnels. 



