62 NEMATODA. FAMILY ANGIOSTOMIDAE 



2 mm. in length and 0.5 mm. in width. Larval stage, 

 Echinococcus polymorphous or hydatid of man which may 

 attain the size of a child's head ; found also in cattle, sheep, 

 pigs and numerous other species of mammals; hydatid cyst 

 composed of outer layer of striated cuticula and inner 

 protoplasmic germinating membrane and is filled with 

 fluid; daughter cysts may be formed internally or externally; 

 numerous scolices are formed in brood capsules within cyst ; 

 over 50 per cent of hydatids in man found in the liver; may 

 also develop in lungs, kidneys, cranial cavity, genitalia, 

 organs of circulation, 'spleen, etc. ; growth of cyst produces 

 symptoms depending on organ involved; found whenever 

 man is closely associated with dogs, especially in cattle or 

 sheep raising countries; especially prevalent in Iceland and 

 Australia. 



Possibly Echinococcus multilocularis a type of hydatid 

 found especially in Russia, Germany and Switzerland, should 

 be considered as a separate species. 



6. NEMATODA 



A. Definition 



Nematodes or round worms, bilaterally symmetrical^ 

 unsegmented; digestive system with both mouth and anus; 

 no true coelom but a large body cavity is present between 

 the body wall and digestive tract; sexes separate; body 

 covered with thick cuticula; reproductive organs simple 

 tubular. The nematodes will be taken up according to the 

 families which have human representatives. 



B. Family Angiostomidae 



Small nematodes; characterized by heterogeny; each 

 species having a parasitic filariform generation alternating 

 with a bisexual, free-living, rhabditiform generation. 



