108 
widel}" separated from the outer membrane. There is thus consider- 
able similarit}^ between the eggs of Ilymenolepis Janceolata and II. 
fUmirivta. The outer merihrane of the former, however, does not 
become thickened as in the case of the latter, but remains very thin, 
and the intervening substance between the two membranes is less con- 
spicuous, and does not ordinarily present the appearance of a third 
membrane as is usual in the latter instance. The inner niemlyrane 
occasionally presents polar papillae as in II. diniinuta and II. nana. 
The egg measures, according to Railliet (1893), 50 by 35 yu, and the 
embrvonal hooks, according to Krabbe (1869), 8 g. According to ni}" 
own measurements the outer membrane varies from 60 to 100 y in 
diameter, the inner measures 30 by 25 y to 40 by 25 yu, and the hooks 
from 12 to 15 y. 
DEVELOPMENT AND LIFE HISTORY. 
Mrazek (1896, p. 11) mentions some cvsticercoids which he found in 
various small crustaceans of the famih^ Cyclopidee. These c^^sticer- 
coids agreed as to the form and size of the hooks with II. hmceolata.^ 
and Mrazek accordingly considered them the intermediate stage of the 
tapeworm under discussion. He gives no description or figures, 
merelv remarking that the cvsticercoids are almost exactlv similar to 
those of Teenia setigera. 
Dadai (1900a) found a large number of specimens of a cercocystis 
(figs. 126-130) in small Crustacea, I) iaptonius sgnnosus Dadai, collected 
from stagnant pools in Yadkert, Hungary, which he would identif}" 
with Ilymenolepis {Drei?anidot8enia) lanceolata (Bloch). 
The c}vst is more or less spherical with a remarkably thick wall, the 
circular and longitudinal muscle layers being remarkabh^ well devel- 
oped. A few calcareous corpuscles were seen in the inner layer of 
the parenchyma of the cyst wall. The cyst measured 0.23 to 0.28 
mm. in length, and U.18 to 0.23 mm. in diameter. 
The head was occasionally seen extruded through the anterior open- 
ing of the cyst (fig. 128), but usually was found retracted and filling 
the cavity of the cyst almost entirely (figs. 126, 127). The rostellum 
was either retracted into the scolex or protruded. The number (8) 
and the form of the hooks (fig. 127) was the same as in II. lanceolata.^ 
but their size Avas A^eiw difi'erent, 55 to 60 yw, while in the latter they 
measure only 31 to 35 u, which renders the correctness of Dadai’s 
identification rather doubtful. 
The caudal appendage is remarkable for its Ajeiy great length.' Its 
surface is very frequently marked by ring-like corrugations. It con- 
sists chiefly of granulated protoplasm and sometimes of masses of 
parenchyma cells; running lengtliAvise through its center is a char- 
acteristic thread-like structure^ Avhich consists of a dark, finely granu- 
lar layer of protoplasm surrounding a still darker central fiber (fig. 
127). 
