103 
EXTERNAL ANATOMY. 
The length has been given as 30 to 130 mm. ; the width posteriorly 
may attain a maximum of 18 mm., more commonly 7 to 12 mm. The 
strobila gradualh^ increases in width from before backward , reaching 
its greatest width a short distance anterior of the posterior extremity, 
then becomes narrower ag'ain and rounded off posteriorily, thus giving 
the worm its characteristic lancet shape (tigs. 108, 110). In the 
anterior portion of the strobila the segments are 30 to 35 times as 
broad as long; in segments with mature reproductive organs the ratio 
between length and breadth is 1 to 10; in the last segments, 1 to 25. 
The head (figs. Ill, 112), Avhich is A^ery small in comparison to the 
rest of the worm, possesses a retractile rejsteUum armed Avith a single 
crown of hooks, usually 8 in number (fig. 113). The hoohs (fig. Hi) 
have a long dorsal root, a short A^entral root, and a prong equal in 
length to about two-thirds of the dorsal root. They measure 31 to 
35 )a (Krabbe, 1869). The short necli, together with the head, is 
often retracted into the anterior part of the strobila. The segments^ 
about 300 in number, in specimens 85 or 90 mm. in length (Zschokke, 
1902a, b), are A^eiy much broader than long throughout the strobila. 
The genital gloves open on the right-hand margin of the strobila, near 
the anterior border of each segment.^' 
INTERNAL ANATOMA'. 
The internal anatomv of the head has not been studied. 
Calcareous bodies are numerous, especially in the cortical paren- 
chyma. 
Nervous systeae — The lateral longitudinal nerves are situated lat- 
erad of the longitudinal excretory A^essels: each main lateral neiwe is 
accompanied by tAvo accessorv neiwes — one dorsal and one ventral 
(fig. 117). 
Muscular system.- — The usual subcuticular muscle fibers are pres- 
ent, 2m outer circular and an inner longitudinal layer. Dorso-ventral 
muscle dhers likewise are present, and are A^ery powerfully developed. 
The Avell-deA^eloped longitudinal rnusde system (/. 7>/., tig. 121) is 
arranged mosth^ in two layers, AAUth about 90 to lOO (Wolff'hugel, 
1900b) or 200 (Zschokke, 1902a, b) bundles in each layer. In the 
cortical parenchyma, i. e., betAA^een the outer muscle layer and the 
cuticula, there are numerous scattering longitudinal muscle fibers. 
Lying inside the inner layer in both the dorsal and the A^entral hah^es 
of the strobila there are tAvo bundles of muscle fibers, one on each side 
of the median line, separated by a space equal to about one-sixth the 
«Dujardin (1845a, p. 562) describes the pores of Tsenia lanceolata as irregularly 
alternate, mentioning also the presence of 10 hooks on the rostellum; two circum- 
stances Avhich indicate the probability that he had under observation another 
species. 
