HALOMENIA GRAVIDA. 149 



are developed into a complicated series of ridges. In the customary position 

 a distichous radula is present and though of small size is typical in all essential 

 respects. It rests upon a delicate though perfectly distinct basement membrane 

 and is produced by odontoblasts at the bottom of a shallow sac. There are, 

 so far as may be determined from cross sections, about twenty-four rows of 

 teeth which present the appearance represented (Plate 34, fig. 12). 



On each side of the forward limits of the radula sac the narrow ducts of the 

 ventral salivary glands open into the digestive tract and on the other hand lead 

 right and left into a reservoir extending far toward the dorsal side of the pharynx. 

 Each of these cavities is surrounded by a gland (Plate 22, figs. 2, 5), composed 

 of multitudes of small, pj'riform cells grouped, by means of delicate connective- 

 tissue septa, into lobules of various sizes. The ductule from each cell makes its 

 way to the wall of a reservoir into which it pours its granular, moderately stain- 

 ing secretion by way of an intercellular opening. 



Beyond the radula the alimentary canal courses dorsally and opens into 

 the stomach-intestine. In front of this junction a coecunv extends far forward 

 and as noted previously develops on each side of the mid line diverticula which 

 pierce the body wall and come in contact with the under side of what appear 

 to be modified papillae. These are developed also by the stomach-intestine 

 throughout its entire extent. A further peculiarity of the mid gut exists in the 

 form of numerous small secondary outpouchings of the wall of the ordinary 

 gut pouches which give in cross section a complicated appearance to this region 

 (Plate 22, fig. 3). The dorsal wall of the intestine, in contact with the gonad, 

 is relatively low and heavily ciliatetl. .Vt the level of the forward pericardial 

 wall the gut narrows rapidly, loses its glandular character, becomes ciliated and 

 by a relatively small pore opens into the cloaca. 



The position of the heart, its relation posteriorly to the branchial folds and 

 anteriorly to the aorta are typical. As is seen (Plate 3, fig. 5) it consists of two 

 divisions united bj^ a small canal apparently provided with a valve. Both 

 portions are moderately muscular, and lodge in the meshes of the muscle bands 

 numerous large, irregular cells which have the appearance of blood forming 

 elements. The aorta, extending anteriorly and dorsal to the gonad, supplies 

 the last named organ with many well-defined ventral branches which, as in 

 P. hawaiiensis , pass ventrally along the mid line and reaching the neighborhood 

 of the gut course outwardly and then dorsally to unite with the larger spaces 

 beside the aorta. In the head region this main vessel communicates as usual 

 with sinuses which carry the blood in turn to spaces between the gut and body 



