MOVEMENT OF INVERTEBRATES 



123 



Perhaps the simplest form of movement is tliat already 

 described in the Amoeba, where a lobe or pseudopudium is 

 thrust out and the body of the animal 

 slowly flows after it. It is, of course, an 

 incredibly slow means of progression, 

 and the advance made in twenty-four 

 hours is well under one foot. 



The slipper animalcule, Paramoe- 

 cium, swims by means of a coating 

 of cilia, and if you could magnify 

 a Paramoecium to the size 

 of a pony, it would move 

 about as fast as a pony 

 galloping. As a rule sea-ane- 

 mones are fairly stationary, 

 though they sometimes creep a- 

 bout by expanding or contracting 

 their muscular foot or base. Jelly- 

 fish swim through the water by 

 extending and compressing their 

 hollow umbrella, like the opening 

 and shutting of a parasol. The free- 

 living flat- worms known as Tur- 

 BELLARiA movc through the water 

 both by means of cilia, which cover 

 their skin, gliding, or by creeping like 

 a slug. The creeping is brought about 

 by waves of muscular contraction. 

 They will also swim freely by a wave- 

 like contraction passing along their 

 flattened body. Although the adult Fm. 41. Paramoerium mu- 

 flukes, Trematoda, and tapeworms, t['"\'^^^u^'''\ "\7"^r'^^; 



' . .. . ^ . . After liiitsclili. 1. .Mouth at 



Cestoda, are parasites livmg with not bottom of groove. 2. Gullet, 

 much movement in the body of some 3. Food vacuole just iH-ini^ 

 host, usually a vertebrate, their larvae f°™^'- |; SSS^t^^ 

 are capable of considerable movement, stiniiing hairs which have 

 and indeed they need to be or they exploded: the unexpI.Mied 



ij r> J 1 ^-i-„ "0^,,..^ ones line the cuticle. (>. ("ilia. 



would never find new hosts. Round- „ ^^^^^ ^^^^j^^^ g^ ^^„^^^„ 

 worms, which again are largely internal uucleua. 9. Contractile fibrils. 



I 



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