327 
1906-7.] Helix pomatia with Paired Male Organs. 
so closely resemble the corresponding structures figured by Plate in the 
primitive Pulmonate, Pythia scarabeus, that these organs may be described 
as having identical relations in the two forms, except that in the supple- 
mentary organs of Helix the vas deferens has no actual opening at its 
epidermal end and that it bears a flagellum which is not present in Pythia. 
It is suggested that the supplementary organs of Helix, having been able 
to develop free from the disturbing influence of the vagina, oviduct, and 
their accessory structures (which on the right side have been secondarily 
moved forwards in phylogeny), have assumed a condition closely resembling 
that which they would present in the ancestral form in which male and 
female apertures were some distance apart. The form of the extra organs 
(the vas deferens having a close connection at one end with the epidermis), 
which, it is suggested, might also be assumed by the corresponding normal 
organs if they were also free to develop independently of the female 
structures, supports the view that the present condition of the genital ducts 
in Helix and in other Stylommatophora, has been derived from a condition 
existing in the ancestral form in which the vas deferens and penis were 
connected with the primitive genital opening by means of a lateral groove, 
such as is still found in Pythia. 
10. Consideration of this and of other abnormalities which have been 
described in the Pulmonata leads to the conclusion that the penis develops 
as an epidermal structure which in Helix and other Stylommatophora is 
closely associated with, and is secondarily carried inwards by, the invagin- 
ating atrium. In proterogynously hermaphrodite forms, especially in those 
in which the shell is depressed, reduced, or absent, the development of the 
penis rudiment may be postponed until the male elements in the gonad are 
further developed. 
ADDENDUM. (August 3, 1907.) 
After this paper was in type a record of another abnormality, present- 
ing a close parallel to the one described On pp. 312 to 317, was brought to my 
notice by Professor Simroth. Meisenheimer (Pteropoda, in Wiss. Ergebn. 
Deutsch Tiefsee-Exped. auf dem Dampfer “ Valdivia ,” 1898-1899, Bd. ix. 
pp. 290-291, text-fig. 32 : Jena, 1905) describes a single example of the 
gymnosomatous Pteropod Halopsyche gaudichaudi, Souleyet, in which there 
are two penes symmetrically placed on the right and left sides of the buccal 
mass. The internal genital organs are quite normal, and the genital 
duct opens to the exterior on the right side of the body. From this 
aperture a seminal groove leads forwards to the vas deferens and penis 
