The rapidity with which developnient occurred varied in diherent 
individual'?. In general, after d. 5. or 8 day.-?, tapeworms 3. 5. or 8 min. 
long were found — that is. either with simply a long neck, or with evi- 
dent proglottid>. After 15 days, tapeworms were found containing 
mature eggs: after 30 days, the eggs heg^an 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 many or few 
segments were given, had no effect on the results. Rats already har- 
boring /tana also proved refractory to further infection. 
It i^ in the villi of the last loto 12 cm. of the small intestine that the 
intermediate stage develops. As in O./yuris rer//iicalaris, however. 
46 47 48 
49 
50 51 
.cal:. 
Yf ^T.cat/. 
y»T.eai 
a 
Fig?. -KV49. — II. nana. Enlarged. (After Griissi ct Rovelli. 1892a. pi. 3. figs. 4-7, respectively.) 
Figs. -30. 51.— Hexacanth embryos of H. lunia. with primary cavity: calc., calcareous corpmscle: ottnl.. 
caudal appendage: pr. cai\. primary cavity. Enlarged. ' .After Gras^i A- Rovelli. l''92ii. pi. 3. tig'. 
9. respectively. i 
the action of the digestive juices of the upper part of the alimentary 
canal seems necessary liefore the embryo will hatch. Consequently 
the eggs, as they escape from ripe segments into the intestine, do not 
vontinue developing, but pass out unchanged with the feces, and devel- 
opment does 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 designate 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 
cercocy.^tis in a single villus, normally so oriented that it." 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 intestine (tig. hi). 
