556 REVIEW. 



from one another. I am still in doubt as to whether the 

 ductules in the cells of the main lobe enveloping the duct near 

 A (woodcut, Hirudo) are in direct communication with those 

 of the cells enveloping the other duct running parallel to it,, 

 viz. the duct near b ; the former are larger and less branched 

 than the latter, still I believe that communications exist. It 

 is notj however, my intention to review my own work in 

 detail here; I am dealing with M. Bolsius. He considers it 

 impossible for the duct to enter twice the same mass of cells. 

 I can only say that I am satisfied that a continuous duct in 

 its windings does pass twice through the anterior limb of the 

 main lobe, and must add that preconceived notions of possi- 

 bilities must give place to facts. I confess that I do not see 

 much difficulty about it. The arrangement is not very dif- 

 ferent from that which obtains in the nephridium of Lum- 

 bricus, where different limbs of a continuous intra-cellular 

 duct get bound together into one mass. It is still more like 

 what I hope shortly to show to be the structure of the nephri- 

 dium of Moniligaster, where the duct passes two or three 

 times through a mass of cells, themselves penetrated by 

 arborescent ductules. 



M. Bolsius confirms Lang's opinion that the ductules open 

 into the ducts at various places : Schultze and I deny the 

 existence of these communications. It is a mere matter of 

 observation, and it is difficult to argue the point. M. Bolsius 

 and Lang both express surprise at the rarity of these com- 

 munications, but neither of them states how often he thinks 

 he has observed them; certainly, if such communications 

 occur, one would expect them to be very frequent. I have 

 seen several places in sections where one might imagine such 

 a communication to exist, but a moment's reflection will show 

 how easily such an appearance might be produced in sections. 

 In fresh specimens, where the duct and ductules have both 

 been very clear, I have never seen any appearance whatever of 

 a communication. The most difficult portion of the organ to 

 observe in regard to this matter is the apical lobe, where the 

 duct which comes from the recurrent lobe has very thin walls, 



