WAITE : ANTENNAL GLANDS IN IIOMARUS AMERICANUS. 161 



about 2.5 cm. in front of, and 4 cm. ventral to, the bases of the first 

 antennne. The posterior and median sides of the tubercle are more ele- 

 vated from the general surface than are the anterior and lateral sides. 

 The truncated face of the tubercle is a circle with a diameter of about 

 1 mm., and is covered with a membrane which has concentric markings. 

 The actual orifice is situated in the centre of this membranous area, and 

 is less than 0.1 mm. in diameter. The opening into the tubercle from 

 the main cavity of the appendage, as may be seen by inspecting the 

 inside of a moulted shell, is semicircular, the anterior edge being straight ; 

 from this edge a toothed process of the shell, serving for the attachment 

 of muscles, projects backward. 



The blood supply of the antennal gland is mainly from two sources : 

 (a) the antennal artery (arteria lateralis of Gerstaecker) ; {h) the ster- 

 nal artery. The antennal artery arises directly from the heart, and 

 passes obliquely forward and downward close to the dorsal body wall. 

 In that part of its course wliere it runs near the vesicle, it gives off 

 several small branches, which are distributed to the lateral wall of this 

 organ. This artery sends branches into the gland proper at three re- 

 gions : (1.) As the artery passes ventrad along the anterior face of the 

 antennal flexor muscle, a large branch is given off, which goes on the 

 lateral and ventral side of this muscle (i. e. outside of the muscle), and 

 enters the lateral region of the posterior lobe of the gland on its ventral 

 face, to which region it is distributed. (2.) As the antennal artery 

 passes ventral to the lateral anterior lobe of the gland it sends several 

 small branches into the ventral face of this lobe ; and one large branch 

 to the bottom of the hilus, whence it passes dorsad to be distributed to 

 the eudsac (Plate 1, Fig. 1, art. sac). This branch Marchal ('92, 

 p. 1G2) terms the ^'artere sacculaire." (3.) From the dorsal branch of 

 the antenna] artery a small branch is given off, which runs ventrad and 

 mediad to enter the median anterior lobe of the gland. It enters on 

 the ventral face close to the anterior edge. The antennal artery after 

 giving off the artery to the endsac passes into the second antenna. In 

 the region of the coxo-basal joint of this appendage two small branches 

 are given off to the walls of the duct and to the tissues at the base of 

 the tubercle. 



The second source of blood supply is the sternal artery. A branch 

 from this artery comes to the median surface of the posterior lobe, where 

 it divides. The larger of the resulting branches enters the extreme pos- 

 terior region of the lobe on the ventral face close to the edge ; the 

 smaller passes forward along the edge of the gland and enters the ven- 



