EXTERNAL ANATOMY. 
The length has been given as 30 to 130 mm. ; the width posteriorly 
ma}" attain a maximum of 18 mm., mo]’e commonly T to 12 mm. The 
strobila gradually increases in width from before backward, reaching 
its greatest width a short distance anterior of the posterior extremity, 
then becomes narrower again and rounded otf posteriorilv, thus giving 
the worm its characteristic lancet shape (hgs. 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), which is very small in comparison to the 
rest of the worm, possesses a retractile rosteUum armed with a single 
crown of hooks, usually 8 in number (fig.* 113). The hoohs (fig. Ill) 
have a long dorsal root, a short ventral root, and a prong equal in 
length to about two-thirds of the dorsal root. They measure 31 to 
35 yw (Krabbe, 1869). The short necle, 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 very much broader than long throughout the strobila. 
The genital gloves open on the right-hand margin of the strobila, hear 
the anterior border of each segment.^' 
INTERNAL ANATOMY. 
The internal anatomv of the head has not been studied. 
Calcareous bodies are numerous, especially in the cortical paren- 
chyma. 
Nervous system. — The lateral longitudincd nerves are situated lat- 
erad of the longitudinal excretory vessels; each main lateral nerve is 
accompanied by two accessory nerves — one dorsal and one ventral 
(fig. 117). 
Muscular system. — The usual subcuticular muscle fibers are pres- 
ent, an outer circular and an inner Irmgitudinol layer. Denso-ventral 
muscle iiheis likewise are present, and are very powerfully developed. 
The well-developed lemgitudinal muscle system (/. m.. fig. 121) is 
arranged mostly in two layers, with about 90 to lOO (Wolfi'hugel, 
1900b) or 200 (Zschokke, 1902a, b) bundles in each layer. In the 
cortical parenchyma, i. e., between 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 ventral halves 
of the strobila there are two 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 Txnia lanceolata as irregularly 
alternate, mentioning also the presence of 10 hooks on the rostellum; two circum- 
stances which indicate the probability that he had under observation another 
species. 
