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genital duct from its earliest appearance, for in many cases the rest of the 
genital apparatus is quite normal. Yon Jhering (1885, p. 207) remarks 
upon the frequent absence of the male apparatus in specimens of Limax, 
and Simroth (1883-1885, p. 223) describes three specimens of Agriolimax 
laevis as being purely female,* though the one figured (Taf. 9, fig. 22H) 
shows a small papilliform rudiment of the penis but no trace of vas 
deferens.f Simroth (1890, pp. 21, 22) also figures two examples of Vitrina 
lamarcki which show different phases of reduction of the male apparatus. 
In one case (Taf. 2, fig. 11) the penis is quite rudimentary in the form of a 
small nodule on the wall of the atrium ; it has no retractor muscle and no 
connection with the sperm-duct. The figure (Taf. 2, fig. 10) of another 
example shows a penis only slightly larger, without a retractor muscle, but 
the vas deferens opens into it. A similar condition to this last is also 
figured by Simroth (1891, p. 228, and Taf. 9, fig. 13) in a specimen of 
Plutonia atlantica. Collinge records specimens of Helix aspersa (1893, 
p. 237), Avion intermedins (1893, p. 238), and A. hortensis (1904, p. 15), 
in which the male organs are wanting; in the two latter the common duct con- 
sisted of oviduct only. It is possible that in some of the cases above mentioned 
the animals concerned were young and proterogynously hermaphrodite, and 
that although the male organs had not yet made their appearance, they would 
have done so later. Babor’s observations (1894) show that this is probably 
the case in Agriolimax laevis . All the young examples (not more than 
2 cm. long) of this slug which he examined (1894, p. 56) possessed only 
female genitalia, and the gonad contained only ova or ova along with a few 
spermatogonia. After further growth the penis and its annexes were 
formed upon the atrium, and so the hermaphrodite organs became complete. 
In two large specimens, 4 cm. long, the penis was hypertrophied and the 
gonad was purely male. Limax maximus is also proterogynous, but even 
young animals have a rudimentary penis although the gonad at this time 
contains ova only (loc. cit., p. 57). When they have reached their definitive 
size, the animals are hermaphrodite or male, the gonad swarms with 
spermatozoa, and the penis is large. Babor (p. 58) concludes that in most 
Limacidae there is a cycle of development, the animal being at first unisexual 
(in the cases above cited — female), then hermaphrodite, and finally again 
unisexual (male, in the cases cited). 
The examples described by von Jhering, Simroth, and Babor are there- 
* The gonad contained ova only. 
t Simroth (1892-1893) recorded a specimen of Limax primitives in which a retractor 
muscle was attached to the wall of the atrium, but there was no penis. Babor (1894, p. 57), 
however, having examined this example, concludes that a penis is present. 
