MINUTE STRUCTURE OF GILLS OF PAL^MONETES VARIANS. 75 



On the Minute Structure of the Gills of 

 Palaemonetes varians. 



By 



Edgar J. Allen, B.Sc, 



University College, London. 



With Plate X. 



KowALEvsKY^ states that when he injected Palaemon with a 

 strong solution of litmus, two red stripes appeared on the axis 

 of each gill, the effect being due to the colouring matter 

 having been deposited in two solid strings of cells, which lie 

 on both sides of the axis, near the channels through which 

 the blood flows from the gill lamellae to the heart (branchio- 

 cardiac canals). Professor Weldon drew my attention to this 

 statement, and suggested that I should endeavour to work out 

 the minute structure of the gills, of which no description, so 

 far as I am aware, at present exists. My observations have 

 been carried on chiefly upon Palaemonetes varians, as this 

 form can be more readily obtained alive and kept in confine- 

 ment in London. 



Methods. — The gills of Palaemonetes are somewhat difficult 

 to preserve. The use of sublimate and of alcohol failed to 

 give satisfactory results. Specimens preserved in picro -nitric 

 acid, although better, were not good. By using strong 

 Flemming's solution I was, however, finally able to obtain 

 preparations which showed both cell-outlines and protoplasmic 

 structure in an excellent state of preservation. The time 



1 "EinBeitrag zur Kenntnis der Exkretionsorgane," ' Biol. Centralblatt,' 

 Bd. ix, No. 2, 1889, p. 38. 



