404 FEANK E. BEDDARD. 



the flat-worms. Great stress is laid upon the structural 

 identity of the Platyhelminth excretory system with the 

 "head kidney" of larval Polygordius, Chaetopods, and 

 Gephyreans. In both there is a system of fine branched tubes 

 formed of perforated cells, which unite to form a pair of wider 

 tubes opening on to the exterior ; the internal apertures open 

 through a single cell, the so-called "flame cell;" in many of 

 the larval forms the peculiarly modified flame cell is absent, 

 but the aperture is plugged by a single cell. In the Hiru- 

 dinea and Oligochseta there is no longer a special anatomical 

 resemblance to the Platyhelminth ; but this is due to the 

 rudimentary condition of the larval excretory organ, rudi- 

 mentary because there is no free swimming larva. 



Another argument is drawn from the apparent independence 

 of the larval and permanent excretory organs in Annelids ; the 

 fact that in many cases there is no connection between the 

 larval nephridia and those of the adult, and the want of any 

 confirmation of Hatchek's statements to the contrary, indi- 

 rectly favour the hypothesis. 



Again, it is pointed out that while the larval nephridia of 

 Polygordius lie in the head cavity, the persistent nephridia 

 lie in the ccelom ; and these two cavities are not similar. On 

 the other hand, the Platyhelminths have no true ccelom, only 

 a series of minute clefts and spaces in the mesodermic tissue 

 with which the flame cells are connected, and which form a 

 "primary body cavity," comparable to the primary body cavity 

 or head cavity of the Annelid larva. 



Dr. Bergh's conclusions largely depend upon his own 

 researches into the nephridia of Hirudinea; these have 

 been recently criticised by Whitman (15), who meets Bergh's 

 assertion that the larval nephridia have no connection with the 

 permanent nephridia by an equally positive assertion that 

 they have. With regard to the larval excretory organs of the 

 Oligochseta, which have been discovered by Vejdovsky (13) in 

 a variety of types, it is to my mind a significant fact that they 

 occur at the anterior end of the body where no permanent 

 nephridia are developed ; furthermore, these organs lie in the 



