40 
reduced to the point of di.sappearance, or at most containing but very 
little fluid, except behind, where it is in relation Avith the tail, in which 
region it remains large and may contain cells of stellate form. The 
tail has not increased in length, and still bears embryonal hooks. 
Without meaning therelw to establish any homology, (f rassi compares 
this stage to a gastrula. The anterior opening thus corresponds to a 
blastopore, the secondary cavity formed by invagination to an entero- 
coele. and the primary cavity lying between the outer and the inner wall 
to a blastocoele. The outer wall, analogous to the ectoderm of a gas- 
trula. is verv thin, consisting of an irregular laver of more or less 
flattened cells, and, external to this, a thin cuticula. The inner wall, 
analogous to the entoderm, is irregular and thick, apparently lined 
internally with cuticida. The rostellum preserA es the shape it had in 
the former stage, but as a result of the invagination of the anterior 
part of the body now lies posterior of the plane of the suckers 
In the next foil ov' tug stages (flgs. 61. 63, 64) the suckers haA^e moA'ed 
backAvard. and the anterior opening of the secondary caA'ity has closed 
over. 
At later stages (tigs. 65, 66), reached 40, 5o, or Tt» hours after inges- 
tion, the scolex is deflniteA formed. It remains attached l)ehind to 
the inner Avail by a peduncle. A little bridge of cuticula still indicates 
the ]Alace where the anterior opening of the secondary cavity has been 
closed over. The rostellum ma}^ be seen in a state of extension. Tlie 
deflnitiA^e hooks have not yet appeared. The tail persists unchanged 
Avith the embryonal hooks. 
In a still later stage, reached in 80 to 90 hours after ingestion, the 
hooks haA’e appeared on the rostellum. and the excretory A^essels, 
become evident (flg. 58). 
The next stage seen Avas that of the young tapeworm, with short 
neck and no trace of segmentation, attached to the epithelium of the 
A'illus. 
No obseiwations were made regarding the manner in A\diich the 
cercocA^stis leaA'es its position in the villus, and becomes transformed 
into the adult Avorm. 
Not ouIa^ AA’as the rapidity of development found to A*ary in diflerent 
rats, but A^arious stages Avere found occurring simultaneously in the 
same host. 
Attempts Avere made to infest human subjects with eggs and mature 
segments both from man and from rats. Experiments Avere made 
upon eight persons, but except in one,case the results were negatiA^e. 
This case Avas that of a boy flA^e years old, Avho, 15 days after ingesting 
seA^eral segments of Ilyinenolepls nana from a rat, began to pass eggs 
in his feces, and after the administration of an anthelmintic, expelled 
about 50 Avorms. Another instance might be mentioned here, in 
AA^hich a boy, Avho. to judge from fecal examinations, Avas free from 
