Clinical Anatomy of the European Hamster 
one inguinal pair) become prominent (Figs. 1-10, 
1-11) (Nehring, 1901). Furthermore, in contrast to 
the relatively large round prepuce of the males, the 
clitoris has a pointed shape with only a very small 
urinary opening {orificium urethrae externum). 
Before sexual maturity as well as during hiberna- 
tion, the vagina is closed by a layer of squamous 
epithelium in both wild and laboratory bred ham- 
sters (Illman, 1968; Kayser and Aron, 1938; Jahn, 
1968). 
Males and females have a sac-like cutaneous or- 
gan in the umbilical region, the umbilical glandular 
organ (Fig. 1-12, 1-13). 
It consists of compound sebaceous glands covered with a very thick 
epidermis (Vrtis, 1932). * 
Bilaterally, at the level of the anterior process of 
ilium, the European hamster has dark cutaneous 
stripes 2 cm long and 2 mm wide (Vrtis, 1930), the 
so-called flank organs (Fig. 1-14). 
On their surfaces, the flank organs have a thin epidermis under 
which compound sebaceous cells are located. These cells, especially 
active in sexually mature males, produce a secretion by which the 
hamsters mark their territories (Petzsch, 1943; Eibl-Eibesfeld, 1953; 
Petzsch and Petzsch, 1968; Sulzer, 1974; Pidoplicka, 1928; Kristal, 
1929). 
Beneath the epidermis of the umbilical glandular 
and the flank organs, as well as between the glands, 
is abundant melanin which, because of its dark 
brown color, may be externally identified from 
earliest youth (Fig. 1-17). 
1.2 PHYSIOLOGY OF REPRODUCTION 
Wild European hamsters observe a seasonal 
sexual cycle. Their mating season begins around 
the end of April and ceases in the first weeks of 
August (Petzsch, 1937). During this time, the 
females demonstrate a regular estrus cycle consist- 
ing of the following four stages: proestrus (a few 
hours), estrus (1 to 2 days), metestrus (a few hours) 
and diestrus (4 to 6 days) (Reznik-Schiiller, et ai, 
1974a). The females are willing to mate only dur- 
ing estrus, since they demonstrate marked aggres- 
sive behavior towards males in the other three 
stages. The European hamster has a distinctive 
mating behavior. The pronounced foreplay is quite 
extensive and requires a great deal of space. During 
foreplay, the female runs in a figure eight while the 
male follows closely behind, uttering a mating call 
which increases in loudness with the female's readi- 
ness to mate. Finally, the hamsters copulate several 
times before mating is completed. 
Pregnancy lasts from 18 to 21 days and the young 
remain sucklings for about 30 days. Depending 
upon the annual variation of temperature, the 
European hamster hibernates from about the mid- 
dle of October to the middle of March. Breeding of 
the European hamster (Fig. 1-15) has been under- 
taken to obtain animals of a defined age and pedi- 
gree for experimental purposes (Mohr, et ai, 1973; 
Reznick-Schiiller, a/., 1974a). 
The variation in aggressiveness of the females 
during their estrus cycles and the great demand for 
space throughout foreplay and actual mating has 
been considered in developing a breeding method. 
Laboratory-bred hamsters have gradually lost their 
seasonal sexual cycles and observe no hibernation 
when kept under standard laboratory conditions. 
Pregnancy has shortened to only 15.5 to 17 days. 
The females deliver young from 2 to 5 times per 
year and litters are born in each month of the year. 
In addition, the laboratory-bred European hamster 
shows neither aggressiveness towards man nor 
members of its own species. Contrary to wild Euro- 
pean hamsters which are reported to live only 
solitarily (Petzsch, 1937; Eibl-Eibesfeld, 1953), 
the laboratory bred animals can be kept in groups 
(Fig. 1-16) and develop a social order with the 
largest male dominant (Fig. 1-17). 
1.3 PRESENT DISTRIBUTION OF 
EUROPEAN HAMSTERS IN EUROPE 
The European hamster, an animal species which 
had been recognized as a pest by the agricultural 
community, was a menace especially around the 
turn of the century. However, today we know of 
only a few small areas where this animal has not 
yet been exterminated and where it can, at definite 
periods of time, be found in great numbers. 
The results of a general inquiry concerning the 
presence of European hamsters in Germany, which 
was distributed throughout the entire Federal Re- 
public by a questionnaire in a specialty magazine 
for hunters, are pictorially represented on the fol- 
lowing geographic map (Fig. 1-18). Within the 
boundaries of the Democratic Republic of Germany, 
the European hamster is found in the regions es- 
2 
