321 
1906-7.] Helix pomatia with Paired Male Organs. 
sponding normal organs, since the results are so similar in the two cases. 
But on the left side the penis and its annexes have been free to develop 
without the disturbing influences of the vagina, oviduct, and their accessory 
structures, which, on the right side, have been secondarily moved forwards, 
in phylogeny, into the sphere of the male copulatory organ. Under these 
circumstances the supernumerary organs would be more likely to assume a 
condition more closely resembling that which they would present in the 
ancestral form in which the male and female genital apertures were some 
distance apart, and in which, consequently, the male organs developed free 
from the disturbing elements introduced in later forms by the shifting 
forwards of the female aperture and its associated structures. 
The form of these extra organs (the vas deferens having a close 
association at one end with the epidermis) which it is suggested, by 
the above argument, might also be assumed by the corresponding normal 
organs if they were likewise free to develop independently of the female 
structures, supports the already well-established view that the present 
condition of the genital ducts in Helix and 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 aperture by 
means of a lateral groove, such as is still found in Pythia. 
The supernumerary genital organs have also a significance in relation to 
the ontogeny of the male genital apparatus. It is very difficult to reach 
a definite conclusion concerning the mode of development of the male 
organs of the Pulmonata from a study of the published accounts ; evidently 
the conditions are complicated and vary considerably in different genera or 
even species. 
Eisig (1869), working on Limnaea auricularis, concluded that the 
genital apparatus is formed in three separate sections which afterwards 
become connected together : (1) the ovotestis and the hermaphrodite duct ; 
(2) the oviduct, its glands and the prostatic part of the vas deferens ; and 
(3) the penis and the lower (or distal) part of the vas deferens. The penis 
arises as a solid ingrowth from the epidermis, and the vas deferens is 
formed as a diverticulum from the free inner pole of the penis. According 
to Rouzaud (1885) the whole genital apparatus of Pulmonates is the 
product of a single cellular bud on the inner side of the wall of the neck 
region at a point which later becomes the site of the common genital orifice 
in the Helicidae and of the female pore in the Limnaeidae. The penis arises 
as a secondary bud, which in Helix is situated upon the primitive bud, but 
in Limnaea upon the wall of the neck region a short distance from the 
primitive bud. Rouzaud attributes the separation of the penis rudiment in 
VOL. XXVII. 21 
