110 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



as will be easily seen if Figs. 1 and 11 are compared. In A. Shinneri 

 (Semper, pi. xii, fig. 7) the penis is very much, attenuated, and of 

 scarcely larger diameter than the retractor muscle. I at first thought 

 this extreme attenuation of the penis to be due entirely to the 

 immaturity of the specimen, but later, on dissecting some undoubted 

 adults of this species, the same conditions were found to exist. 



With the exception of A. Shinneri, the penis in the other forms is 

 of relatively enormous size. Its internal structure is of considerable 

 interest, and is of use for classificatory purposes, since it constitutes 

 the most striking and constant difference that is observable in all the 

 species. I will, however, defer the description of these differences 

 until later. The retractor muscle of the penis is terminal in position, 

 its distal end being attached to the body-wall on the left side of the 

 animal. 



The ovotestis or hermaphrodite gland (PI. IX, Fig. 1, h.g.) lies 

 imbedded in the right lobe of the liver, and communicates with a very 

 much convoluted hermaphrodite duct (It.d.) ; this shortly enters the 

 albumen gland {a.g.). Tying on the concave border of the albumen 

 gland, and eonnected with the hermaphrodite duct, is a small rod like 

 body, which I will, for the time being, designate the hermaphrodite 

 crccurn (Ji.c). 



This structure is very constant in all species of Acarus, and, 

 from its invariable presence, would seem to be of some functional 

 importance. Semper has not indicated it in any of his figures of 

 the genitalia of Acavus. It is very closely applied to the albumen 

 gland, and, in preserved specimens, so similar in colour, that it may 

 easily have been overlooked by him. 



Such a structure is by no means unique, but on the contrary 

 appears to be of very common occurrence in terrestrial Pulmonata, 

 for on looking through Binney's ' figures of the genitalia of terrestrial 

 molluscs I was struck by the number of forms possessing a similar 

 structure. In the majority of these figures this appendix is repre- 

 sented as a paired, or bilobed, structure, whilst in Acavus it appears 

 unpaired. 



Simroth 2 has figured a similar unpaired organ in the genitalia of 

 Neohyalimax, occupying exactly the same position that it does in 

 Acavus. He calls the structure a seminal vesicle. 



A careful examination of serial transverse sections through this 

 tubular body, however, revealed the paired nature of the structure 

 (PL IX, Tig. 9). The two tubes lie side by side, and are enveloped in 

 a common muscle-sheath ; they communicate with one another (Fig. 8) 

 before opening into the hermaphrodite duct. Each tube is lined 

 with ciliated epithelium ; a few spermatozoa were present in the 

 lumen, but were not sufficiently abundant to suggest that this organ 

 might function as a storing chamber. The albumen gland (a.ff.) is 



1 " Terrestrial Mollusks and Shells of the United States," vol. v (1878). 



2 Proc. Malac. Soc. Lond., vol. ii (lS'JOj, p. 41, pi. v, fig. 9. 



