WAITE : ANTENNAL GLANDS IN HOMAEUS AMEPJCANUS. 159 



color corresponds with the extent of the endsac ; that of the darker 

 border, with that part of the dorsal face of the labyrinth which is not 

 covered by the endsac, or which shows through the attenuated edge of 

 the endsac. 



From the median anterior lobe there is given off a smaller lobe 2.5 to 

 3 mm. in diameter and 5 to 6 mm. in length. This is directed caudad 

 and ventrad, and tapers to a point. Its general shape is conical. In 

 color it is so distinct from the other parts of the gland that Marchal 

 ('92, p. 159) has called it the white lobe. The tapering point opens into 

 the excretory duct in a region ventral to the centre of the gland. This 

 opening is not single, but consists of several minute pores, to each of 

 which there leads one of a series of converging tubules which are in turn 

 formed by the confluence of other smaller tubules in the basal part of 

 the white lobe. These pores are on the dorso-median wall of the duct, 

 2 to 3 mm. from its external orifice. By these the products of the gland 

 are discharged into the duct. This is the only communication which the 

 gland proper has with its accessory structures, there being no direct com- 

 munication between the gland and the vesicle, as there is in Astacus. 

 Therefore the vesicle must be filled by the backing up of the secreted 

 products in the duct from the point where the pores open, a process 

 which is presumably effected by closure of the external opening of 

 the duct. 



The vesicle is situated in the cephalothorax at the side of the masti- 

 catory stomach. Its anterior end lies against the muscles of the body 

 wall. On its median face it presses against the stomach, while poste- 

 riorly it reaches the hepato-pancreas and extends between its lobes. 

 Ventrally, it is in part closely and firmly attached to the dorsal face of 

 the gland (Plate 1, Figs. 1, 2, par. vs.). Posterior to the gland it lies 

 free upon the floor of the cephalothorax. Its shape is roughly oval, its 

 long axis lying in a parasagittal plane. Usually the posterior end is 

 slightly divided into two blunt lobes. Since the thin elastic walls easily 

 conform to the surrounding organs, its actual shape in detail is irregular, 

 depending upon the state of its own distention and that of the stomach, 

 hepato-pancreas, and reproductive organs, and the contraction or relax- 

 ation of the muscles in this region. In some individuals it seems to 

 fill every niche of unoccupied space ; in others there are considerable 

 spaces between it and the body wall. 



I have found no ligamentous attachments for holding the vesicle in 

 place other than that to the dorsal surface of the gland, already noted, 

 and those to the blood-vessels and nerves which come to its surface. 



