EXCEETOEY TUBULES IN AMPHIOXUS LANCEOLATUS. 495 



most varied aniline colours, I finally adopted a colouring 

 agent recommended me by Dr. Hugo Eisig, of the Naples 

 Zoological Station, which answered the purpose better than 

 any other stain. This was a solution of picric acid in turpen- 

 tine, which has the advantage that after mounting the sections 

 they need not be passed through weak alcoholic solutions. 

 Though this stain, however, shows up the carmine well, it 

 does not stain the nucleus or cell-wall diflferentially, so that in 

 making the drawings I had to fill up most of the details from 

 specimens stained with different colours, such as Bismarck 

 brown, carmine, or hsematoxylin. In sections coloured in 

 this way I was able to make out these excreting tubules, but 

 in the case of Amphioxus a very large number of individuals 

 must be used to determine any point definitely, owing to 

 the different appearance almost every individual presents, due 

 to differences of contraction of the gill bars, distention by the 

 genital products, and shrinkage during the killing, hardening, 

 and embedding. 



I have thus not been able to settle clearly whether these 

 tubules just described have any internal opening to the coelom, 

 a point which is of very great interest. Still, to be true 

 nephridial tubules they need not retain permanently a com- 

 munication with the coelom, and they may subsequently be 

 found to possess such continuity at some stage in their develop- 

 ment. 



They may, on the other hand, be simply upward extensions 

 of the atrium, though to this view I should not be very ready to 

 give my support, owing to their bend downwards and their rela- 

 tion to the blood-vessel, which in all parts of its course seems 

 to run outside the atrial and inside the coelomic epithelium. 



The cells, too, are devoid of one marked characteristic of the 

 atrial epithelium, namely, the pigmentation, though this might 

 be due to specialisation. 



If these tubules are coelomic in origin they would come very 

 near true nephridial structures. Indeed, they would be very 

 typical segmental organs devoid of any connecting duct, and 

 their only difference from the most primitive form of nephridia 



