154 PLAT VHELMINTHES. 
The outer surface of the body is covered by a thick 
cuticle, underneath which is a layer of 
ectoderm in which the cell-walls are said 
to be absent. This ectoderm is thickened in the mid- 
dorsal, mid-ventral, and the two lateral lines, corresponding 
to the four external lines. Below the ectoderm is a single 
layer of longitudinal muscle-cells, divided into four sections 
by the four ridges of ectoderm. Each muscle- 
cell has an outer muscular part with longi- 
tudinal striation and an inner protoplasmic part with a 
nucleus. As in Aydra, only a portion of the muscle-cell is 
differentiated into contractile tissue. 
The nervous and excretory systems are best seen in 
sections. The former consists of a nerve-ring round the front 
of the pharynx which is thickened dorsally and 
ventrally. Six small nerves run forwards and 
six others run backwards. Of these the four lateral soon 
become very thin, but the dorsal and ventral run the whole 
length of the body, embedded in the ectodermal ridges. 
They are connected by alternate lateral commissures. 
In the lateral ectodermal ridges there runs a pair of 
excretory ducts which apparently end blindly behind, but 
meet in front to open by the median ventral 
pore a little behind the mouth. 
The male sexual organs consist of a single long coiled 
tube. The blind and tapering end forms the /es¢is, the 
middle part the vas deferens, and the lower part swells out 
to form the seminal vesicle. This opens bya small duct into 
the intestine close to the anus. A small se¢a/ Stand secretes 
the anal sete. The female organs consist of a pair of long 
coiled tubes. The inner part of each forms the ovary, the 
middle portion the ovéduct which swells out to form the 
uterus. The two uteri join in a common vagina to open 
to the exterior by a median ventral opening towards the 
anterior end of the body. 
The fecundity is enormous, many thousands of fertilised 
and encapsuled eggs being discharged daily from the uteri. 
These pass out of the body of the host, but 
; their subsequent history is unknown. It is 
said that, as in the case of liver-rot, the maw-worm is 
acquired by feeding on damp pasture. 
Integumentary. 
Motor. 
Nervous. 
Excretory. 
Development. 
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