WORMS igi 



hooked, blunt, pointed, bent, curved and tapering spines. 1 hey vary 

 not only in shape, size, number and arrangement, but also in many 

 subtle ways such as the proportion of their different parts. A specialist 

 in the Acanthocephala must therefore resign himself to an endless 

 vista of measurements and the drawing of hundreds of little spines. We 

 have estimated that in one publication devoted to this group the author 

 has figured 12,000 spines. 



Tapeworms (Cestoda) 



Tapeworms, as Shipley pointed out, are like recurring decimals. At 

 one end there is a "head" or scolex, which is armed with hooks and 

 adhesive suckers and behind it stretches a long, pallid ribbon of seg- 

 ments which grow out from the "neck" region, each repeating the one 

 immediately behind it. Every segment (proglottid) carries a complete 

 set of organs, and it is, therefore, perhaps more accurate to think of a 

 tapeworm as a long chain of individuals joined together. However, the 

 nerve fibres and muscles extend through the whole length of the body, 

 so if the animal enjoyed any emotions they would be presumably of a 

 communal type. 



Although the anterior or "neck" end is continuously producing 

 segments the tapeworm's length is limited, for at the posterior end the 

 oldest segments are dropping off — having gradually lost their initial 

 structure and degenerated into nothing more than bags of egg? which 

 pass out with the faeces of the host. During the course of its life one of 

 the large species of tapeworm has been known to produce seven kilo- 

 metres of segments. 



Each proglottid carries a complete set of both male and female sex 

 organs, sometimes two of each. These are so arranged that each seg- 

 ment can fertilise itself but it is not unusual to find the different seg- 

 ments of a much coiled tapeworm having simultaneous sexual inter- 

 course at a number of points along its length. Everything, in fact, has 

 been sacrificed to communal egg laying, which, admittedly, is highly 

 successful but rather monotonous. One tapeworm has been calculated 

 to produce 36,000 eggs a day and up to two milliard during its entire 

 life. 



Tapeworms have no alimentary canal and their food is absorbed 

 through the outer surface of the body. It has been suggested that during 



