W. Heape 
223 
muscular, and that they are probably derived directly from the con¬ 
nective tissue parenchyma of the animal. 
I cannot be certain, for reasons already stated, regarding the 
longitudinal fibres. Their concentration into bundles indicates they 
may be more highly specialised than the more scattered contractile 
fibres, but in the absence of all muscular structure there is presumptive 
evidence of their similarity with the dorso-ventral fibres. This view is 
to some extent borne out by the facts that the longitudinal bundles are 
very variable in size and extent (compare Figs. 3 and 4), that the fibres 
are very similar to the dorso-ventral fibres at their thickest part, and 
that the bundles are not enclosed in a sheath. 
We have then five stages of the development of contractile fibres 
before us here. First, the processes of the connective tissue parenchyma 
cells are contractile; secondly, the superficial and internal processes of the 
superficial layer of connective tissue cells have increased contractile 
power; while thirdly, the circular fibres; fourthly, the dorso-ventral fibres; 
and fifthly, the longitudinal fibres exhibit graduall}' increasing and more 
highly specialised development of this function. 
On the whole then it may be contended that the supporting structure 
of the body of T. elliptica is to be regarded as a plasmodium of 
connective tissue, the elements of which are somewhat concentrated on 
the surface of the body, and are also here and there differentiated into 
processes or fibres with specially powerful contractile properties; the 
whole is bounded by a delicate basement membrane and enveloped in a 
cuticle. 
DESCRIPTION OF PLATE XVII. 
c. Cuticle. 
b. m. Basement membrane. 
par. Connective tissue parenchyma. 
s.c.t. Superficial layer of connective tissue. 
s.l.f. Superficial longitudinal contractile fibres. 
l.f. Longitudinal contractile fibres, in bundles, situated deeper in the body. 
c. f. Circular contractile fibres. 
d. v.f. Dorso-ventral contractile fibres. 
Fig. 1. Section through proglottis of T. elliptica, showing division of body into dorsal, 
central, and ventral sections and the situation of the contractile apparatus. (Osmic 
acid ) 
Fig. 2. The specimen from which this section was made was swollen dorso-ventrally and 
contracted in length. The superficial layer of connective tissue cells are elongated and 
crowded together, they are connected superficially with the basement membrane by 
