No. I.] GERM-LAYERS IN CLEPSINE. 163 



unknown, Bergh (No. 30, p. 115) was led to believe that 

 " die Segmentalorgane typisch segmental, ohne die geringste 

 Verbindiing taitereinander entstehen." In regard to the relations 

 of the larval to the permanent nephridia, Bergli says : "Bei den 

 Blutegeln tritt mit grosser Klarheit hervor, dass Urnieren und 

 Segmentalorgane durchaiis nichts niiteinander zu thun haben. 

 Letztere legen sich namlich (in den Rumpfkeimen) erst an 

 nachdem die Urnieren sichschon langevon diesen abgelost haben. 

 Ebensowenig kann von einem urspriinglichen Zusammenhang 

 zwischen den einzelnen Anlagen der Segmentalorgane die Rede 

 sein (No. 30, p. 113). 



If we examine Bergh's Fig. 5, PI, XII. (No. 9), in the light 

 of what we now know about the origin of the nephridia, we see 

 at once that the provisional nephridia arise from one or both of 

 the cell-rows, which must be identified with the nephridial rows 

 of Clepsine. In this figure, the fourth nephridium (" Urniere ") 

 of the left side is represented by a single cell, which still re- 

 tains its original position in the outer nephridial row. It is thus 

 highly probable, if not quite certain, that both the larval and 

 the permanent organs do arise from the same basis, — the 

 nephridial rows. Allowing this to be the case the relations of 

 the two sets of organs would be very clear. One thing is per- 

 fectly certain : it can no longer be said with Bergh and 

 Vejdovsky (No. 31, p. 123), that the permanent nephridia arise 

 from disconnected bases or rudiments. 



The view first advanced by Hatschek (No. 25), in spite of the 

 theoretical objections raised by Balfour (No. 32, pp. 565-6) and 

 the lack of confirmation on the part of other writers, is, after all, 

 the one most easily reconciled with the results presented in this 

 paper. In my opinion it not only accords better with known 

 facts, but presents a more rational basis for explaining the mor- 

 phogenetic relations of these organs, than the theory of discon- 

 nected rudiments. I refer, of course, not to the details of the 

 conditions described in Polygordius, but to general features ; such 

 as, the derivation of the whole excretory system of the head and 

 trunk from a common basis, and the formation of the trunk 



(30.) Bergh, R. S. Die Exkretionsorgane der Wiirmer. Kosmos. II. p. 97. 

 18S5. 



(31.) Vejdovsky, F. System und Morphologic der Oligochaeten. Prag, 1884. 



