THE MICROSCOPE IN AETIOLOGY. 337 



20 to 25 mm. long, and head; in the male spiral, in the 

 female straight. Generally found in the colon of children 

 or adults. 



27. Trichina Spiralis.Ou the second day after eating 

 raw flesh containing trichinae, and after digestion of the 

 inclosing capsule, the worm is sexually mature Copula- 

 tion occurs, and on the sixth day after the females bring 

 forth each about 1000 filamentous embryos. These pierce 

 the intestinal wall and wander through the tissues to the 

 voluntary muscles, where they coil up spirally and be- 

 come encysted. The cysts may become hard and even 

 calcify. In this state they may remain for years capable 

 of development. The hog is considered the original 

 bearer of trichinae, whence they have infected other ani- 

 mals. 



4. Family. Filaridce. Long filamentous body. 



28. Filaria Medicensis. Threadworm. Guineaworm. 

 Inhabits the subcutaneous tissue of the foot. Found only 

 in tropical countries. 



3d Class. Annelidce. Ringed worms. Cylindrical or 

 flattened. Segmented body with brain, oesophageal ring, 

 chain of abdominal ganglia and bloodvessels. 



Order Hirudinis. Leech. Body with narrow rings 

 and terminal disk. No feet. Hermaphrodite. 



Sub-order Gnathobdellce. Gill-leach. Throat with three 

 often dentated gills. A sort of oval sucker disk in front 

 of the mouth. Blood mostly red. 



29. Hirudo Medicinalis.tiO to 90 fine teeth on the 

 free border of the gills. Is three years in arriving to 

 sexual maturity. 



III. ARTHROPODA. 



Animals laterally symmetrical. Bodies segmented. 

 Limbs articulate. Brain and abdominal ganglia present. 

 Propagation generally sexual. 



22 



