8 The Molluscan Family Planorhidae 



From the base of the cup, and piercing the integument of the pre- 

 putium, is a duct of variable length (DC) , which, if long, is folded on the 

 outside of the preputium (plate 27, fig. 9, Helisoma campanulatum) ; or, 

 if short, simply lies on the surface of the preputium (plate 23, fig. 2, 

 Helisoma anceps) . When coiled on the outside of the preputium it is bound 

 to that organ by short muscles. Sections through the cup are shown on 

 plate 23, fig. 1, plate 24, fig. 1, and plate 27, fig. 1. The duct terminates 

 at the muscular ring or diaphragm (D), pierces the wall of the lower part 

 of the vergic sac, and terminates just above the ring (plate 23, fig. 6, 

 Helisoma anceps; plate 24, fig. 10, Helisoma trivolvis) , or in a groove in 

 the ring (plate 36, fig. 9, Parapholyx effusa) . 



The function of the penial gland is at present insufficiently known. It 

 was once thought by the writer to be connected with the formation of the 

 spermatophore and was called the spermatophore gland (Baker, 1931, 

 p. 581), but this belief scarcely agrees with the structure of the gland. In 

 section this organ is seen to have two parts, each of which may have a 

 different function. In Helisoma trivolvis (plate 24, fig. 4) the gland shows 

 a large cup-shaped cavity, the walls of which are lined with vertical folds 

 (GF). The bottom of this cup is. lined with folds laid crosswise. The long 

 duct begins at the bottom of the cup and terminates in the vergic space 

 (DC) of the vergic sac (VS) just above the muscular ring or dia- 

 phragm (D). 



In some species, as Helisoma duryi and its varieties, the duct begins in 

 a small cavity or cup at the end of the gland (plate 33, figs. 3, 10), the 

 walls of which have vertical folds. The larger cup-shaped cavity has no 

 connection with the smaller cavity or its duct. In some species, notably in 

 the genus Menetus, there is no external duct, connection with the vergic 

 space being effected by an open channel (plate 42, figs. 3, 4). Another 

 group of Menetus has a short duct on the inside of the preputium (plate 

 39, fig. 7). In Menetus and some other groups there is a small channel in 

 the muscular ring (plate 39, fig. 7, D). Helisoma anceps shows this feature 

 well (plate 23, figs. 2, 6). Parapholyx effusa klamathensis (plate 36, figs. 

 9, 10) also shows the canal in the muscular ring. 



It appears possible that one of the functions of the penial gland might 

 be to expand the opening in the muscular ring or diaphragm which is 

 normally nearly or quite closed, and prepare it for the protrusion of the 

 verge. The penial gland duct possibly carries a fluid, secreted by the ver- 

 tical folds in the gland cup, to the diaphragm to facilitate the passage of 

 the verge. 



But there is another function of the gland. It has been observed that 

 during copulation not only is the verge extruded from the male opening, 

 but also the whole penial gland. This has been observed in many species of 

 Helisoma (H. duryi normale, plate 33, fig. 16; H. trivolvis lentuni, plate 29, 

 figs. 7, 11, 12; Promenetus exacuous, plate 41, fig. 9). In all species of 

 Planorbidae the verge is extruded during copulation. In a specimen of 

 Drepanotrema lucidum examined (plate 11, figs. 1, 2, 6, 7) the verge and 

 penial gland protruded together from the male opening. It is probable that 

 the gland portion with the cup-like cavity lined with vertical folds is an 

 excitatory organ or sarcobelum, for in the species possessing this gland 

 there is no special apparatus for this purpose such as occurs in other species 



