AND EMBRYOLOGY OF LIMULUS. 17 



like mass (a), extending along close to the great collective vein, and attached to 

 it by irregular bands of connective tissue, which also hold the gland in place. 

 From this horizontal mass, four vertical branches {h, b) arise, and lie between and 

 next to the partitions at the base of the legs, which divide the latero-sternal region 

 of the cephalothorax into compartments. The posterior of these four vertical lobes 

 accompanies the middle hepatic vein from its origin from the great collective vein, 

 and is sent off opposite the insertion of the fifth pair of feet. Half-way between the 

 origin of the vein and the articulation of the limb to the body, it turns at a right angle, 

 the ends of the two other lobes passing a little beyond it, and ends in a blind 

 sac, less vertical than the others, slightly ascending at the end, which lies just above 

 the insertion of the second pair of feet. The two middle lobes are directed to the 

 collective vein. Each lobe is somewhat flattened out, and lies close to the posterior 

 wall of the compartment in which it is situated, as if wedged in between the wall 

 and the muscles between it and the anterior portion of the compartment. Each 

 lobe also accompanies the bases of the first four tegumentary nerves. 



I could not Ijy injection of the gland discover any general opening into the coelom 

 or body cavity, or perceive any connection with the hepatic, or with the great collective 

 vein. The four lobes end in blind sacs, and have no lumen or central cavity. 



The lobes are irregular in form, appearing as if twisted and knotted, and with sheets 

 and bands of connective tissue enclosing the muscles, among which the gland lies. 

 Each lobe when cut across, is oval, with a yellowish interior and a small central cavity. 



The gland externally is of a bright brick-red. The mass is quite dense, though yielding, 

 and on this account hard to be cut with the microtome. 



When examined under Hartnack's No. 9 immersion lens and Zentmayer's B eye-piece, 

 the reddish external cortical portion when teased out from the living animal, is seen to 

 consist of closely aggregated, irregularly rounded, nucleated cells of quite unequal size ; 

 and scattered about in the interstices between the cells, are dark reddish pigment masses 

 (plate 3, fig. 7a) which give color to the gland. They are very irregular in size and form, 

 and twenty hours after a portion of the living gland was submitted to microscopic examin- 

 ation moved to and fro. In other portions of the outer reddish part of the gland, where 

 the pigment masses are wanting, the mass is made up of fine gi'anular cells, which have 

 no nucleus. Other cells have a large nucleus filled with granules, and containing nucleoli. 



In the yellowish or medullary portion are scattered about very sparingly certain 

 spherical cells which probably are purely secretory (plate 3, figs. 76, 7c). The nucleus is 

 very large and amber colored, with a clear nucleolus ; others have no nucleolus, and the 

 small ones are colorless. 



I am at a loss to think what these glands, with their active secreting cells filled with a 

 yellowish fluid, can be, unless they are renal and excretory in their nature. In general 

 position they coincide with that of the shell glands of the Entomostraca and Branchi- 

 opoda, including the Phyllopoda, especially as worked out in Leptodora, by Weismann.^ 

 But in lacking apparently an excretory duct, and in their dense pareuchym, with no 

 lumen, as well as histologically, they seem to differ from the shell glands of the lower 



' Uebor den Bau unJ Lebenserscheinungen von LeptoJora hyallna. Zeitscbr. fur wiss. Zoologie, Bd. xxiv. p. 385, 1874. 



