Tapeworms of Birds 
398 
the posterior margin of the proglottis. Vesicula seminalis absent. Cirrus 
armed with fine spines. Female organs as in D. proglottina with the 
exception of their later development. Shell-gland present. Uterus 
developed but not persistent. Eggs in parenchyma, not in egg- 
capsules. Diameter of egg 0-033 mm., of onchosphere 0-023 mm. 
Life-History . Experiments have been made with a view to working 
out the life-history of this species, but so far have only given negative 
results. According to Grassi and Rovelli (4), the intermediate hosts of 
D. proglottina are the slugs Limax cinereus Lister, L. agrestis Linn., 
and L. variegatus Drap. It was thought therefore that as D. pro¬ 
glottina appeared to be the nearest species to D. dubius, slugs would 
probably be the intermediate hosts of the latter. Feeding experiments 
were therefore made with as many varieties of slugs as could be obtained. 
The chief obstacle was the heavy mortality amongst them when kept 
in captivity. The slugs employed were kept in large earthenware pots, 
the bottoms of which were covered with moist earth upon which stones 
were placed. In order to prevent them from escaping, tine muslin was 
placed across the top of the pot. The whole was then placed in total 
darkness. Cabbage and potato were found to be the best foods. Yet 
in spite of all care culture after culture died off, and often it was 
found that when one came to record the experiment the slugs were 
already dead. That slugs undoubtedly eat tapeworms was proved by 
Miss Lebour (6) and by eggs being found in their intestines. Dissections 
and sections however never showed the slightest trace of developing 
cysticercoids. 
Altogether 5 Arion ater L, 6 A. hortensis Fer., 18 A. circumscriptus 
John., and 45 Agriolimax agrestis L. were fed and examined, the time 
elapsing between the first date of feeding and the dissection varying 
from 10 to 35 days. These slugs were the only ones found in the 
fields, and of these only Arion circumscriptus and Agriolimax agrestis 
were common. It therefore seems to indicate that slugs are not the 
intermediate hosts. In the case of life-histories, however, a negative 
result should only be accepted with suspicion since there are so many 
causes operating unfavourably. In the first place it is not possible in 
dealing with such small forms to ascertain before use that the tape¬ 
worm eggs are mature and fertilised. Next it cannot be proved that 
all the slugs, or that even a small minority, will eat the eggs, in spite 
of the latter being smeared over the food. Again, considering the heavy 
mortality, it is probable that the infected slugs would be amongst 
those first to die and would consequently be overlooked. And. lastly, 
