Studies on the Development of Larvai Nephridia. 489 



eülarged flame-cell, the tube of the flame-cell answering to the canal 

 of the heacl-kidney. Thus the head-kiduey, the nephridium of the 

 first segmeut of those Polychaeta that pass throiigh a Trochophoial 

 stage, never develops beyond the flame-cell cooditioii. 



Beyoud this mere resemblance therefore, there are reasons for 

 regardiug the flame-cell type of nephridium as the most primitive, 

 and as being derived phylogenetically from the flame-cells and 

 protonephridia of lower forms. 



The present work was undertaken in the hope of proving this 

 011 a basis of development. It has been my flrst aira to study the 

 origin and growth of the flame-cells, the characteristic feature of the 

 larvai nephridium. For these cells Goodrich (0 pag. 442) has re- 

 cently proposed the name of "Solenocyte", by which it is best to 

 designate them in future. If vee compare them with the flame-cells 

 of Nemertines as described by Bürger, the resemblance is remarkable. 

 There is the same arrangement of the cell body at the end of a fine 

 canal dovs^n which their cilia work, the celi body itself throwing 

 out a number of processes. The comparison of some of the figures 

 given in the follovnng paper with the drawings of the excretory 

 orgaus of Drepanophorus given by Bürger (2) brings ut I think a 

 number of striking resemblances. (Compare figs. 5, 6, 7 of Bürger's 

 pajìcr with figs. 11, 16 and 25 of the present paper.) 



At present it is perhaps premature to speculate regarding the 

 amount of morphological iraportance to be attached to these soleuo- 

 eytes. Their wide distribution in the class of the Polychaeta, and 

 their presence in such widely separated forms as Amphioxus, the 

 Polygordius and the Actinotrocha larva, is significant in itself. 



A review of a few of the facts, that bave been brought to light 

 on the development of the excretory organs, is sufficient I think to 

 convince anyone, that up tili now, we bave been confusing under 

 the name of nephridium two orgaus of very diflerent character and 

 origin. One distinctly coelomic, the genital duct and its funnel, the 

 other the true nephridium, which is not necessarily coelomic but 

 may be separated from the coelovii altogether. It is true the nephridium 

 may, and often does, come into relation with the coelom; this is a 

 secondary modification and not the originai condition. The first and 

 most important function of the coelom has alwaj's been the develop- 

 ment of the genital cells, the renai excretory function has been acquired 

 later. It is only after this has taken place that the nephridia come 

 into relation with it, when the two organs, genital duct and 



