The developmeut of the uriuogenital organs of the lamprey. 45 



tendency in the anterior segments to approach a metameric arrange- 

 ment (conf. Field 1892 and 1894). Although I have not been able 

 to find the very first traces of the mesonephric tubules in larva) of 

 the same age as those in which Fürbringer found them (9 mm in 

 length), I have, nevertheless, seen the young tubules in larvœ only 

 12 mm long extending over only 2 or 3 segments and here the number 

 of tubules (II or 12) is already so far in excess of the number of 

 segments, that I am forced to regard Fürbringer's statement as 

 erroneous. 



Concerning the condition of the glomeruli of the mesonephros 

 there has been much difference of opinion. Wilhelm Müller (1875) 

 observed the isolated round glomeruli in Aramocœtes 25 mm long 

 (corresponding to the stage of my Fig. (iö) and in larvae 43 mm 

 long. Fritz Meyer (1876) found in the adult lamprey only a single 

 glomerulus 9 cm long and 25 mm broad and deep. Fürbringer (1878) 

 fails to confirm Meyer's statement but finds even in the adult "eine 

 reichliche Anzahl von getrennten Glomerulis". Schneider (1879) 

 differs only apparently from Meyer since he admits that in the adult 

 the different glomeruli "liegen allerdings in einer Säule" which is very 

 probably what Meyer saw and described as a single glomerulus. 

 Vialleton (1890) distinguishes two regions of the mesonephros, a short 

 anterior in which the glomeruli are "soit isolés soit groupés en petit 

 nombre, mais jamais disposés en série continue" and a longer poste rif)r 

 region in which the glomeruli are united to form a "veritable colonne 

 glomérulaire" in the sense of Schneider. I understand from Vial- 

 leton's description that the tubules newly arising at the posterior 

 end of the second region add their glomeruli successively to the al- 

 ready existing glomerular column. At least he says nothing about 

 finding isolated glomeruli behind the main column. Bujor's statements 

 agree in the main with Schneider's. 



The lack of agreement in the accounts above cited is in part 

 due to a misinterpretation of the facts and in part to a study of 

 different stages. The confusion seems to be still further increased 

 by the fact that the word "glomerulus" is not used in a fixed 

 sense. As understood in other Vertebrates it means the tuft of vas- 

 cular loops which is invaginated into and pushes before it the flattening 

 wall of a nephric tubule. As I have shown, this definition will apply to 

 Fetromijson as well. The tubule ends at first in a blind sac which is 

 pushed in by the capillary network, so that the whole end of the 

 tubule together with the capillary structure is a true Malpighian 



