258 DISEASES DUE TO HELMINTHS 



Two ovaries develop, connected by a common oviduct which joins 

 the spermatic duct. This latter is then joined in turn by the common 

 duct of the yolk gland and the ducts of the shell gland, then it passes 

 on to the uterus. This latter is usually a blind tube but it may be 

 open by a special aperture. 



^^^hen the uterus is full of eggs it fills up the proglottis, and the 

 male organs atrophy and disappear. Hence : — 



In the first segments no sexual organs are seen. 



In the slightly mature segments the male organs are made out 



first. 



In the more mature segments the female organs develop as the 



male organs diminsh. 



In the fully mature segments the male organs have disappeared. 



THE LIFE HISTORY. 



The mature proglottis can fertilize itself or another segment. 



The spermatozoa pass along the spermatic duct, meet the ovum and 

 fertilize it. The ovum then receives its yolk and shell, and passing to 

 the uterus escapes by the uterine orifice, when there is one, or when the 

 proglottis is destroyed. 



The egg is oval, yellowish with or without an operculum. 



Two membranes are formed, one near the shell, the other near the 

 embryo. The shell and the outer envelope are lost and in the faeces 

 is seen the embryophore in its inner envelope with three pairs of hooks. 

 This is the Onchosphere. 



Some species are ciliated. This onchosphere is then taken up by a 

 new host of a difTerent class, the envelope is then cast oflf, the hooks 

 burrow their way to suitable tissues, after which its hooks are lost and a 

 bladder-like cyst is formed. In the walls of this cyst develops a scolex. 

 This cyst is called the 



CYSTICERCUS. 



From Onchosphere to Cysticercus requires two tOi six months. 



This infected tissue is ingested by another animal, the cyst is 

 dissolved and the scolex develops in a few weeks to an adult tape- 

 worm, which can live for about a year. 



They obtain food by osmosis from the intestine. 



CLASSIFICATION OF CESTODA. 



Order (i) Pseudophyllidea. The scolex may or may not be armed 

 with two groove-like suckers. It has three genital 

 orifices. 



Order (2) Tetraphyllidea. These parasites are not found in man. 



