PLATYVYHELMINTHES 97 
termed proglottides, which increase in size as they recede from 
the head. The body of a tapeworm may be divided into three 
regions: (i.) the head, (11.) the neck, and (iii.) the segmented 
trunk. 
The head of 7. saginata (Fig. 66) is spherical in shape, and 
bears on its sides four well-developed suckers. Other species, 
as 7. soliwm, in addition to the suckers, are provided with a 
double cirelet of chitinoid hooks, which assist the suckers to 
attach the worm to the inner surface of the alimentary canal 
(Fig. 66, C) of its host. The head is mobile, and can shift its 
point of attachment with ease. 
The neck is the region immediately succeeding the head ; 
its most anterior half is not segmented. The first trace of 
division into segments is the appearance of shallow grooves 
which separate the various proglottides one from another. 
As they grow backward the proglottides increase in size, and 
those situated a foot or more behind the head are sexually 
mature. 
The surface of the body is covered by a thin clear struc- 
tureless cuticle, the layer of cells beneath this, corresponding 
with the ectoderm of other animals, is composed of long-tailed 
cells, the tails running down into the parenchyma. The body 
of the tapeworm is practically solid, the coelom being repre- 
sented by poorly-developed splits in the parenchyma. 
The muscle fibres are arranged in longitudinal trans- 
verse and dorso-ventral bundles. The outermost layer, the 
longitudinal, is not a very definite layer, but consists of a 
number of unstriated fibres scattered through the parenchyma. 
The transverse muscles lie immediately within the longitudinal ; 
they serve to divide the parenchyma into a central and a 
cortical portion. The dorso-ventral fibres run from one sur- 
face to the other, and are very irregularly arranged. The 
muscle fibres are non-striated, and often branched at their 
ends. The animal has very considerable powers of extension 
and contraction. 
The parenchyma is composed of ill-defined connective 
tissue cells, amongst which are scattered, especially in the 
cortex, a number of ovoid calcareous corpuscles (Fig. 67), 
about whose function little is known. They have been vari- 
7 
