74 WORMS, ROTIFERS, LEECHES, POLYZOA 



among the fronds of the seaweeds covering the rocks in the tidal 

 pools. They are carnivorous in habit. 



Leptoplana possesses a nervous ganglion or brain of oval shape, 

 subdivided superficially into right and left halves by a shallow 

 depression, and enclosed in a tough capsule. The eyes appear as 

 a collection of small black dots lying at the sides of the brain, and 

 the mouth is almost in the centre of the ventral surface of the 

 body ; no anal opening is present. Through the mouth, a frilled 

 structure, called the pharynx, is protruded when the animal is 

 feeding. This pharynx is supplied with salivary glands, which 

 quickly soften and disintegrate the flesh of the prey, and the 

 food then passes by way of the pharynx into the stomach and is 

 there digested. From the stomach it passes into the lateral branches 

 of the intestine, and finally the insoluble residue is discharged 

 through the pharynx into the water. 



The fresh-water Flat-worms prey upon water insects and 

 pond snails, while the land forms have been observed to prey 

 upon earthworms and snails. 



The Trematoda, many of which are called " Flukes," are 

 flat, rarely cylindrical, often leaf-shaped, or broad, bladder-like 

 creatures, leading a parasitic life within or outside various ani- 

 mals. " Whilst some grow from large eggs, laid about the locali- 

 ties frequented by the parent, into the shape of the adult, others 

 present the phenomena of alternation of generation, compli- 

 cated by curious metamorphoses. These last kinds come from 

 very small eg.gs which have got into water or damp places, and 

 are at first very minute, contractile embryos, sometimes ciliated, 

 which endeavour to settle on some animal or other, ordinarily 

 some of the mollusca. This stage is that of the ciliated embryo. 

 The ciliated embryo's office is to get on to a host ; it then loses its 

 cilia and becomes stationary on its host, and then gives exit to a 

 cylindrical sac-like object, which has two lateral prolongations 

 close to a tapering tail. At this stage of growth the parasite is 

 called the Redid, and it has a mouth and a single intestine, but 

 no other organs. Within this bag-like Redia a process of budding 

 goes on, each bud becoming a creature like the parent of the 

 ciliated embryo in shape ; but it is destitute of reproductive 

 organs, and is furnished with a long, flat tail like a tadpole, by 

 which it is propelled after the escape from the Redia. At this stage 



I 



