38 
The rapidity with which development occurred varied in dilierent 
individuals. In general, after d. 5. or 8 days, tapeworms 3. 5. or 8 mm. 
long were found — that is. either with simply a long neck, or with evi- 
dent proglottids. After 15 days, tapeworms were found containing 
mature eggs: after 30 days, the eggs began to appear in the feces. 
While the results in the experiments with white rats aged from 1 to 
3 months were constant and positive, when rats younger than 1 month 
(suckling) or over 3 months were used the results were either negative 
or only a few tapeworms were developed. Ordinary rats proved more 
refractory to infection than white rats, and the results were generally 
negative, even when the rats were of the favorable age — 1 to 3 months. 
Whether the animal was fasting or well fed. or whether manv or few 
segments were given, had no effect on the results. Eats alreadv har- 
boring Hymen oh i> is j,ana also proved refractory to further infection. 
It is in the villi of the last lt»to 12 cm. of the small intestine that the 
intermediate stage develops. As in (ir-yuris rerinicidcrris. however. 
Figs. 4«>— 19. — H. nana. Enlarged. (After Gras.<i A: Rovelli. 1892a. pi. .3. figs. 4-7, respectively.) 
Fig>. .50.51. — Hexacanth embryos of H. nana. with primary cavitj': calc., calcareous corpuscle: caiaJ., 
caudal appendage: pr. cav.. primary cavity. Enlarged. (After Grassi A: Rovelli. 1892a. jd. 3. ti^G. 
'. 9. respectively. 
the action of the digestive juices of the upper j^art of the alimentary 
canal seems necessarv before the embryo will hatch. Consequently 
the eggs, as they escape from ripe segments into the intestine, do not 
continue developing, but pass out unchanged with the feces, and devel- 
opment doe-; not proceed until they again come into the alimentary 
canal by way of the mouth [ ( or by reverse peristalsis into the stomach]. 
The following observations were made upon the development as it 
occurs in the intestinal villi of the rat (Grassi & Rovelli, 1892a). The 
cysticercoid, or cercocystis, to use the name employed by Villot 
(1882) to de.Agnate those cysticercoids which have caudal appendages, 
is found in a cavity, which represents the much-dilated central lym- 
phatic cavity of the villus. Rarely there are two, ordinarily only one 
cercocvstis in a single auIIus. normallv so oriented that its long 
axis corresponds to the long axis of the villus, with its posterior end 
(that bearing the embryonal hooks) directed inward, i. e., toward the 
lumen of the inte.stine (fig. 87). 
