ORDER TURBELLARIA. 



257 



DEVELOPMENT OF LIVER FLUKE. 



A, sexually mature (after alanchard) ; B, embryo (after 

 Ltuckait). 



produces the ' rot." The effects of allowing flocks of sheep to graze on low pastures, during con- 

 tinuous wet weather, are unfortunately too well known. The animals take in the parasite with their 

 grass, or accidentally consume Mollusca which contain 

 them. 



In the genus Amphistomum the ventral sucker is 

 close to the posterior end, and is deep. The species are 

 found in the frog, ox, elephant, and many other animals. 



The next sub-order or division of the Trematoda is 

 that of the Polystoma, which are furnished with several 

 suckers, the hindmost of which often have hooks. They 

 are parasites on the outside of animals. The eggs are 

 large, and there are no metamorphoses as a rule. In 

 Diplozoon, two Polystoma are found united so as to form 

 ;an X-like creature, and the hinder extremity of each 

 is furnished with two rows of quadruple suckers. 



ORDER TURBELLARIA. 



These are lowly organised flat worms, which may be 

 ribbon-shaped, leaf-shaped, or oval, broad, or long. They 

 live free in water, and on land, are predaceous, and they 

 have a mouth with or without a proboscis, and a simple 

 or ramifying digestive tube. The skin is ciliated, and 

 is highly sensitive. There are eye-spots and rudimentary 

 organs of hearing in some. The anus is present in some, 

 but not in others. The nervous system consists of two ganglia placed in the anterior part of the body ; 

 branches are given off, and a longitudinal cord extends backwards, and in some there are the 

 rudiments of ganglia. In some Turbellaria the limits of the digestive tract are not distinguishable, 

 .and the food finds its way into a mass of internal cells. All have water- vessels which open externally 

 by one or more pores, and are ciliated ; and also "pseudo-haemal " vessels, consisting usually of a median, 

 a a dorsal, and two lateral trunks, which unite in front and behind. 



The walls of these vessels are contractile, non-ciliated, and their 

 contents are clear and uncoloured. One sub-order, the Nemertina, 

 has ciliated grooves on the anterior part of the body, on the floor 

 of which is a nervous structure. In most the embryo passes by 

 insensible gradations into the form of the adult, and in some 

 there is a metamorphosis. There are three sub-orders, the Rhab- 

 doccela, the Dendrocoela, and the Nemertina or Rhynchocoela. 



The Rhabdocoela are the simplest forms, and have a flat body 

 with cylindrical or rod-shaped digestive organs, without a vent. 

 They are carnivorous and suck the juice of small worms and ento- 

 mostraca and insect larvse which they envelop in a secretion. One 

 family, the Opistomidse, has a proboscis, coloured eyes, and 

 calcareous particles connected with hearing. The family Convolu- 

 tidse are long flat worms with chlorophyll in their tissues, and 

 one of the species is a very active dweller between tide-marks in 

 England. It swims well, yet it has no special senses. The 

 Dendroccela have a ramified intestine, and the long flat body has a 

 proboscis. The Land Planarians have eyes, no tentacles, a pro- 

 boscis, and a narrow body. They are found in the United Kingdom and generally in Western and 

 Central Europe. They have been found in America, and on continental as well as on oceanic islands. 

 Moseley states that they are nocturnal in their habits, -and shun the light, getting under leaves. 

 Some contain chlorophyll, and seek the light but die in the sunshine. They eat small snails, worms, 

 and flies. An American kind secretes a mucous thread and suspends itself in the water, and another 

 271 



DIGESTIVE APPARATUS OF EVKYLEPTA 

 SANGUIXOLENTA. 



a, nervous ir.mslion, or brain ; b. mouth ; c. 

 ph&rynx ; </. stomach: e, ramification of 

 the digestive cavity. 



