THE STRUCTURE OF THE LARVA OF LANICE CONCHILEGA 1 1 1 



With regard to the nephridial organs of the Terebellids in gênerai, 

 Ed. Meyer (1887) déclares that the larvse of tins group even when quite 

 young possess a pair of excretory organs, or head-kidneys (Kopfnieren), 

 situated in the cephalic région. They open, according to the writer, exter- 

 nally by a small pore at the side of the body, but hâve no internai opening 

 nor is there a ciliated funnel. The whole tube is somewhat convoluted, and 

 forms a figure S. 



Meyer goes on to say that the larval nephridia persist for some time, 

 but are eventually replaced by permanent nephridia. The larval nephridia 

 are in full activity when the first permanent pair of nephridias approaches 

 completion, and as soon as thèse are capable of performing the gênerai 

 excretory functions of the body, the head-kidney begins to degenerate, and 

 finally disappears, 



We hâve not suffîcient data at présent, to give a complète account of 

 the development of the nephridia in this species, but on comparing the 

 nephridial organs of our larva with those of the very young post-larval 

 forms, we find that a transition of some kind has already taken place in the 

 latter. Instead of there being three separate pairs of nephridia, one pair 

 only of longitudinal ducts are found, having three short ducts leading into 

 them, each of which is provided with a ciliated funnel. We could not find 

 the external openings of thèse nephridia. The posterior pair of nephridia 

 are not yet formed. 



Without the évidence to be derived from the examination of inter- 

 mediate stages, it is impossible to say whether the nephridia found in the 

 post larval and later stages, are new structures or whether they are formed 

 by the coalescence of the larval nephridia. 



According to Meyers view, the anterior nephridia of our larva should 

 represent a temporary » head-kidney ", which on the appearance ofthe per- 

 manent nephridia, dégénérâtes. 



We hâve not however seen any signs of degeneration in this organ. 

 Meyer's figure of the young larva of Polyriinia nebulosa shows us one pair 

 of nephridia, but the stage of development of the larva is very much 

 younger than ours, so that it is possible that the two posterior pairs of 

 nephridia présent in our larva of Lanice represent the anlagen of the per- 

 manent anterior nephridia, but we hâve no definite évidence that this is 

 really the case, and we must leave this interesting point for the présent 

 until an opportunity occurs of obtaining spécimens of intermediate stages 

 of growth. 



