EXCRETORY TUBULES IN AMPHIOXUS LANCEOLATUS. 493 



we find well-marked blood-vessels. This fact lends further 

 support to the very justifiable view that they may have an 

 excretory function. 



A further set of modified atrial epithelial cells are those 

 which cover the outer portion of the gill bars. These are 

 columnar in shape, with a large nucleus near the base, and 

 generally a considerable amount of granules at the opposite 

 end. Definite pigment granules are found only in one or two 

 cells where the epithelium of the alimentary tract borders on 

 the atrial epithelium. 



In the specimens fed with carmine the atrial epithelial cells 

 of the secondary or tongue bars all showed carmine granules. 

 In the primary bars I was unable to distinguish any carmine. 

 This fact is_, I think, to be explained by the circumstance that 

 in the secondary bars the blood-vessel, which I described as 

 running along the outside of the chitinoid rod, lies imme- 

 diately beneath the atrial epithelium, while in the primary 

 bars of course it lies beneath the ccelomic epithelium, and 

 only very fine ramifications, if any, would pass round to the 

 atrial epithelium. 



On staining sections, and also in feeding living individuals 

 with Bismarck brown, the same fact will be observed, the atrial 

 epithelium covering the secondary bars becoming much more 

 intensely stained than the similar epithelium of the primary 

 bars. I made use of this colouring matter on the recom- 

 mendation of Dr. Paul Mayer, of the Zoological Station at 

 Naples, who invariably used it to colour excreting cells, chiefly 

 in Crustacea. 



Similar to the atrial epithelium of these gill bars behaves 

 the epithelium of the dorsalward extension of the atrium 

 lining the so-called suspensory or pharyngo-pleural folds. 

 The cells of this portion of the epithelium are even larger than 

 those of the gill bars in many parts, and stain deeply in their 

 more granular portion with Bismarck brown. 



That so large an amount of the atrial epithelium should be 

 excretory does not seem strange or improbable to me, as Dr. 

 Eisig, in experimenting with Capitellidse, found these worms 



