40 
reduced to the point of disappearance, or at most containing l)ut very 
little fluid, except behind, wliere it is in relation with the tail, in which 
region it remains large and ma}' contain cells of stellate form. The 
tail has not increased in length, and still bears embryonal hooks. 
AVithout meaning thereby to establish any homology. Grassi compares 
this stage to a gastrula. The anterior opening thus corresponds to a 
Iflastopore. 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 (‘ctoderm of a gas- 
trula. is very thin, consisting of an irregular layer 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 cuticula. The rostellum preserves 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 foUcnc tug stagei< (tigs. til. 63. 64) the suckers have moved 
backward, and the anterior opening of the secondary cavity has closed . 
over. 
At later stages (tigs. 65. 66), reached 4n. 5t». or 7<> hours after inges- | 
tion, the scolex is detinitely formed. It remains attached behind to 
the inner wall by a peduncle. A little bridge of cuticula still indicates i 
the place where the anterior opening of the secondary cavitv has been ‘ 
closed over. The rostellum ma\’ be seen in a state of extension. The 
detinitive hooks have not yet appeared. The tail persists unchanged ) 
with the embryonal hooks. 
In a still later stage, reached in So to hO hours after ingestion, the 
hooks have appeared on the rostellum. and tin' ('xcretory vessels 
become evident (tig. 58). 
The next stage seen was that of the young tapeworm, with short 
neck and no trace of segmentation, attached to the epithelium of the ; 
villus. 
No ol)servations were made regarding the manner in which the 
cercoc 3 ^stis leaves its positioji in the villus, and becomes transformed, 
into the adult worm. 
Not onlv was the rapiditv of development found to vaiw in diflerent 
rats, but various stages were found occurring simultaneouslv in the ! 
same host. 
Attempts were made to infest human subjects with eggs and mature 
segments both from man and from rats. Experiments were made 
upon eight persons, but except in one case the results were negative. 
This case was that of a bov live vears old. who, 15 davs after ingesting |j 
several segments of Tlynitnolepis nana from a rat, began to pass eggs i 
in his feces, and after the administration of an anthelmintic, expelled 
about 50 worms. Another instance might be mentioned here, in 
which a boy. who. to judge from fecal examinations, was free from 
