MINUTE STRUCTURE OF GILLS OF PAL^MONETES VARIANS. 81 



to represent the cut ends of fine tubes (fig. 10). It is highly 

 probable that in the natural condition all these tubes are in 

 direct communication with the duct. 



In preparations which have been treated with pyroligneous 

 acid the protoplasm at the apex of each cell and immediately 

 at the base of the fine tube stains much more deeply than the 

 rest of the cell (fig. 9). 



The second form of gland found in the gill (fig. 1, &c., 

 c. gl. ', fig. 13) difi*ers only slightly from the reticulate form 

 already described. The absence of the well-developed net- 

 work in the protoplasm is the feature which most distinguishes 

 it from the latter. The clear glands are also slightly smaller 

 than the reticulate, and it will be noticed (fig. 13) that the 

 nuclei are relatively larger, and are situated more nearly at 

 the centres of the cells. The apex of each cell appears less 

 sharply defined, although with a high power it is not difficult 

 to satisfy oneself as to the presence of a fine tube leading from 

 it. The central nucleus and duct can also be made out. The 

 more darkly staining portion of the protoplasm at the apex of 

 each cell, although less marked, extends further back into the 

 body of the cell, and possesses a more definite outline on its 

 outer margin (fig. 13, d). 



The clear glands are generally (though not invariably, fig. 3, 

 c. gl.) situated in the neighbourhood of the venous channels of 

 the axis, whilst, as already stated, the reticulate glands lie for 

 the most part next to the epithelial lining of the artery. These 

 relative positions are so fairly well maintained that it seems 

 impossible to suppose that the two appearances indicate merely 

 difi'erent conditions of similar glands performing identical 

 functions. 



The presence of glandular bodies in the gill has not, so far 

 as I am aware, been previously observed in any Crustacea. 

 Max Braun^ has shown that glands of a similar form, which 



1 "Ueber die histolog. Vorgange b. d. Hautung von Astacus fluviati- 

 11 s," ' Arb. a. d. Zool. Inst. Wiirzburg,' Bd. ii, 1875. " Zur Kenntniss des 

 Vorkommens der Speichel und Kittdriisen bei den Decapoden," ditto, Bd. iii, 

 1876-7. 



YOL. XXXIV, PAET I. — NEW SEE. F 



