ETJPAGTTRTJS. 523 



In minute structure the gills are seen to be covered 

 by a thin sheath of chitin, beneath which is a single 

 layer of cells, the epidermis. The lamellae consist 

 merely of this epidermal layer with its chitinous invest- 

 ment on both sides, separated by irregular spaces. A 

 distinct vessel — the outer lamellar sinus — runs round the 

 outer edge of each lamella. It is in communication with 

 the cavity of the lamella (the lamellar sinus). The 

 central axis is dumbbell-shaped and besides connective 

 tissue there are two other kinds of cellular structures to 

 be found in it. These are the branchial excretory cells 

 and the branchial glands first described by Allen in 

 Palaemonetes.* There are two kinds of these latter 

 structures, and Allen's observation as to their different 

 positions in the animal he studied holds good for 

 E. bernhardus. The reticulate glands are distinguished 

 by the fact that the cytoplasm of their cells appears as a 

 deeply staining network, the nuclei are spherical and lie 

 near the base, and the ducts and the nuclei belonging to 

 them are very distinct. The protoplasm at the apex of 

 each cell stains deeper with Erlich's haematoxylin and 

 saurefuchsin than the remainder. This type of gland is 

 almost exclusively found round the efferent vessels. The 

 other type of gland is characterised by the absence of the 

 network, the smaller size of the individual cells and the 

 larger relative size and more central position of the 

 nuclei. It is also much more difficult to follow their 

 ducts and distinguish the nucleus of the duct. This type 

 of gland stains very lightly, and is neither so abundant 

 nor so prominent as the reticulate type. It is generally 

 found round the afferent vessels of the gill axis. In 

 general structure these branchial glands are precisely 

 similar to the stellate cells which are present in the 

 * Quart. Journ. M.S., Vol. XXXIV., p. 75, 1893, 



